Here’s an easy recipe for blueberry rhubarb crisp with marzipan crumble, a great way to enjoy the classic combination of blueberries and rhubarb, also known as rhuberry or bluebarb.
In Quebec, rhubarb grows for most of the summer. It comes in much later here than the rest of Canada. The rhubarb in our gardens is usually ready to be picked mid-June, and it continues to grow all the way to August. Since our rhubarb season is that little bit later than in other places, it overlaps quite a bit with the summer berries at the market. And though I love to make desserts with JUST rhubarb (some of my best rhubarb recipes include rhubarb jam, rhubarb bostock, rhubarb pie, this rhubarb cake recipe (with double the rhubarb), and mini orange cakes topped with rhubarb, to name a few!), it’s fun to mix it up too. I keep reading about combining blueberries and rhubarb in desserts so I decided that I, the rhubarb “purist,” had to give the combination a try.
What is “rhuberry” or “bluebarb”?
Turns out, there’s a name for the combination of blueberries and rhubarb, which is referred to as “bluebarb” or “rhuberry”. So, if you ever come across a rhuberry pie or a bluebarb crisp, the recipe author is referring to a dessert made with both rhubarb and blueberry. At first, this seemed like an unusual combination, but then again, blueberries have a mild flavour that really pops in sweet desserts and helps to balance stronger flavours, like astringent, mouth-puckering rhubarb. I think I might like the combination of blueberry and rhubarb in this blueberry rhubarb crisp better than strawberry rhubarb in these strawberry and rhubarb crumbles, though also quite good!
Thickeners for fillings in fruit crisps and fruit crumbles
Just like with pies, the questions that are always up for debate are: what thickener to bake with when making a fruit crisp and how much thickener to use to thicken the fruit filling . There are people that use no thickeners for fruit crisps and crumbles, leading to the cleanest fruit filling flavour without any risk of a potential cloudy look or starchy mouthfeel, which are both very possible since crisps are often baked for less time than pies. This also means that you may end up with a “soupier” fruit filling, depending on the fruit, the ripeness, the bake time, and also the volume of berries/rhubarb used.
There are other people that opt to use very small amounts of thickeners, like flour, cornstarch, or even arrowroot or tapioca starch. The thing is, in a blueberry crisp of this size, with 2 pounds of fruit in the filling, in order for the thickener to do it’s job, you need to make sure the fruit filling, from edge to centre, bubbles and boils, otherwise there is no point. It just won’t gel without enough heat. Trust me. I tested shorter baking times and the results were mediocre.
The question of whether or not you use a thickener is really personal preference. For a dessert like an apple crisp or a peach cobbler, for example, you don’t really need to debate the issue because you can easily get away without a thickener: apples and peaches don’t have as much water as blueberries and rhubarb. With summer fruit like the ones I used here, it’s a matter of personal taste. I prefer no thickener because the flavour of the filling is so clean and bright, and if the filling is properly heated through to the middle, the pectin in the blueberries should do its job of gelling the juices, if you let crumble cool before serving (it took me three batches of crumble to figure this out).
Baking with marzipan? Things to note
Adding marzipan to an oat crumble topping is BRILLIANT, I tell you. Then again, I might not be the most objective critique as I am pretty
obsessed with addicted to marzipan. I love the stuff so much! Anyway, you can buy marzipan in bars or blocks, but be sure to buy a top quality marzipan, preferably of German origin because the Germans make great marzipan. You will know you are buying a good marzipan if they disclose the almond content on the packaging. The marzipan I buy tends to have around 50% almonds. Usually I buy either Lübeckeror or Schluckwerder brand marzipan. The marzipan from Schluckwerder seems to have more almond extract in it and therefore a more pronounced, bitter almond flavour, which I quite like. I used Schluckwerder marzipan for this recipe. In the past, I went with Lübeckeror marzipan for the gorgeous Milk Bar style blackberry almond cake. The marzipan from Niederegger brand has 57% almonds, so it would also be a great option for this recipe (buy it on Amazon). It’s important to read the label of the marzipan because some have as little as 10–20% almonds, the rest being mostly sugar.
The trouble with baking with marzipan is that it burns into something that is rock hard and unpleasant if you aren’t careful. When I tested out this recipe the first time, I mixed together the fruit with the sugar, topped it with the marzipan crumble and baked everything together for 50 to 60 minutes. The marzipan burned on the top and the filling didn’t gel properly because there wasn’t enough time for the filling to boil without burning the crumble. When I repeated the tests, I opted for a two-stage baking process: to bake the filling first for a good 45 minutes, then top the hot fruit filling with the crumble and bake for 30 more minutes to cook the crumble top. This works infinitely better. The marzipan still browns, but it’s a good golden brown, not charcoal black.
Blueberry rhubarb crisp with marzipan oat crumble topping recipe
Blueberry rhubarb crisp with marzipan crumble
Easy blueberry rhubarb crisp with a marzipan oat crumble makes the best summertime dessert to feed a crowd. Make sure to bake the fruit filling first so that it has time to cook and gel properly. The combination of blueberry and rhubarb is also referred to as bluebarb or rhuberry.
Blueberry rhubarb filling
- 100 grams light brown sugar 1/2 cup
- 16 grams tapioca starch, cornstarch or flour ***OPTIONAL*** 2 tbsp
- 50 grams granulated sugar 1/4 cup
- 1/4 tsp fine kosher salt
- 450 grams fresh blueberries 3 cups
- 450 grams chopped fresh rhubarb 4 cups
Marzipan crumble topping
- 150 grams marzipan grated
- 60 grams all-purpose flour 1/2 cup
- 50 grams granulated sugar 1/4 cup
- 50 grams ground almonds 1/2 cup
- 45 grams rolled oats 1/2 cup
- 1/4 tsp fine kosher salt
- 80 grams melted unsalted butter 1/3 cup
Preheat the oven to 357ºF. Butter the inside of a large 10 inch baking dish that is at least 3 inches deep.
Prepare the fruit filling
In a large bowl, combine the sugars with the fine kosher salt. If you are using a thickener, mix it with the sugars to make sure it is evenly dispersed.
Add the fruit to the bowl and toss everything together to coat evenly. Transfer to the buttered baking dish, cover with foil, and bake on the middle rack for 45 minutes, stirring after 30 minutes.
Prepare the crumble topping
In a large bowl, stir together the grated marzipan, flour, sugar, ground almonds, rolled oats and salt. Add the melted butter and mix to form a crumble.
When the fruit has baked for 45 minutes, take the dish out of the oven, give the fruit a gentle stir, then sprinkle the crumble topping over the fruit.
Put the baking dish back in the oven and bake the crumble, uncovered, until it is golden brown and the filling is bubbly, about 30 more minutes.
Let rest before serving.
You may want to set the baking dish on a large cookie sheet or place a cookie sheet on the rack below to catch the bubbling hot fruit juice drips as they may burn on the bottom of your oven.
Please note this post contains affiliate links to Amazon. If you buy a product I recommend, I will get a small commission, and the price you have to pay will not change in any way.
Janice Lawandi is chemist-turned-baker, working as a recipe developer in Montreal, Quebec, Canada. She studied pastry at Le Cordon Bleu in Ottawa and cooking at l’Académie Culinaire. She has a BSc in Biochemistry from Concordia University and a PhD in Chemistry from McGill University.