Old-Fashioned Blueberry Crumb Cake Recipe

There is no smell more welcoming than that of a freshly baked coffee cake coming out of the oven. A dreamy combination of cinnamon, brown sugar, and toasty aromas is enough to lure anyone into sitting down for a slice with a fresh cup of coffee. Although not technically a coffee cake, crumb cake evokes fond childhood memories for me, with crumbly cakes baked by my grandmother and shared with milky cups of coffee and decks of cards. While coffee cake comes in many forms and flavors, with or without crumbly toppings, streusel is the star when it comes to crumb cake. My old-fashioned blueberry crumb cake has an extra-thick layer of crunchy and nutty streusel, enhanced with cinnamon, oats, and rich, brown butter. The cake itself is tender and spongy, made extra moist with sour cream and pockets of plump and ripe fresh blueberries. This cake is delicious warm from the oven, but also keeps well for several days in the refrigerator to satisfy for snacking or a coffee break anytime.

The trick for making your best crumb cake is to avoid over-mixing any part of the recipe. Being old-fashioned, this cake is based on recipes that were once mixed by hand with a spoon, so take care with your mixer. This goes for the crumb topping, as well. The goal is to have some large clumps of streusel that remain after stirring together the ingredients, as these are the best parts of the buttery topping once baked!

To make the crumb topping for your old-fashioned blueberry crumb cake, you will start by making a batch of brown butter, using unsalted butter as your base. You will also need all-purpose flour, light brown sugar, chopped walnuts, old-fashioned rolled oats (not instant), sea salt, and ground cinnamon and nutmeg. Nutmeg adds a wonderful warmth to the topping and pairs perfectly with the walnuts.

For the cake itself, you will need more all-purpose flour, baking powder, baking soda, and sea salt for your dry ingredient mix. You will also need unsalted butter, a whole egg and a yolk, vanilla extract, full-fat sour cream, and maple syrup. Last, you will need some perfectly ripe blueberries to fold into the mix.

Melt the butter for the crumb topping in a small saucepan over medium-low heat, swirling or stirring frequently (about 5 minutes).

Once the butter is foamy and nutty-smelling, and brown flecks appear at the bottom of the pan, pour it into a heat-proof bowl and allow it to cool slightly.

In a separate bowl, combine the flour, brown sugar, walnuts, oats, cinnamon, nutmeg, and sea salt.

Pour in the slightly warm brown butter and toss with a fork until the mixture forms clumps. Set aside.

Preheat the oven to 350 F.

Spray an 8 x 12-inch baking pan with non-stick baking spray.

Cut a piece of parchment paper to fit, with 2 sides long enough to hang over the edge of the pan. These will be used as handles to remove the cake after baking.

In a medium bowl, whisk together the flour, baking powder, sea salt, and baking soda. Set aside.

In a stand or other large mixer bowl, cream together the granulated sugar and softened butter until light and fluffy.

Beat in the egg, yolk, and vanilla extract until fully incorporated.

On low speed, mix in ⅓ of the flour mixture until combined.

Scrape the sides of the bowl down and mix in the sour cream.

Mix in another third of the flour, then the maple syrup.

Add in the final addition of the flour mixture.

Fold the blueberries into the batter by hand.

Transfer the batter to the prepared pan, spreading it evenly to the edges.

Distribute the crumb topping over the top.

Bake the blueberry crumb cake for 40-45 minutes, or until a tester inserted into the center comes out clean.

Cool the cake for at least 30 minutes in the pan on a rack.

Carefully lift the cake out using the parchment overhang as handles.

Cool completely, then slice and serve the old-fashioned blueberry crumb cake.

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Although many of us became familiar with crumb cake in our grandmother's kitchens, or from the box of Entenmann's from the grocer's shelf, its roots likely trace back to Germany. Streuselkuchen dates back to the 19th century, and they were classified as spongy, yeasted cakes with a simple streusel topping of butter, flour, sugar, and cinnamon. The streusel was often marbled into the batter, along with a variety of fresh fruits. Eventually, this humble cake was embraced by bakers in New York City (including Entenmann), who opted for a sour cream-based cake and an extra-thick layer of crunchy streusel on top.

Streuselkuchen, or the subsequent Americanized version of crumb cake, was also born out of an era that focused on home baking rather than bakery purchases for items other than bread. Many European countries have a rich history of "coffee culture," or the practice of enjoying coffee and cake with friends and family as a morning or afternoon break in the day. 

Although this crumb cake is best when made with fresh, sweet blueberries, frozen berries are certainly an option when fresh ones are not available or in season. The most important tip when using frozen blueberries is to keep them frozen until you're ready to fold them into the batter. Otherwise, you will end up with a purple-ish shade that may or may not look very appealing once baked. Once your crumb cake batter is ready to go, take the frozen berries from the freezer and toss them with a tablespoon of all-purpose flour. This will help to keep them separated as you mix them into the batter. Note that using the frozen berries may extend the baking time by a few minutes, so keep an eye on the crumb topping and tent the cake with a layer of foil if it starts to get too brown. 

As for other substitutions in this recipe, there are a few things you can experiment with. In the crumb topping, try using some chopped hazelnuts, almonds, or pecans in place of the walnuts. You can also go nut-free with your crumble. Whole-milk Greek yogurt is a good substitute for the sour cream, and will give the batter an extra-tangy flavor. Whether you go with yogurt or sour cream, don't try using a low-fat or fat-free variety, as the recipe relies on the fat to make the batter rich and moist. Cardamom would be a delightful spice to use in place of or in addition to the cinnamon and nutmeg, as it Cardamom has a floral and citrusy quality that enhances the sweetness of the blueberries.

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