This Chocolate Crumb Cake has all the amazing qualities of New York Crumb Cake: the light cake, the buttery mountain of crumbs, the top layer of confectioners’ sugar...except this time both the cake and the crumbs have cocoa powder added! It could not be more incredible! If that wasn't enough, this mini chocolate cake is gluten free, nut free, eggless and can easily be vegan!
Preheat your oven to 325 degrees Fahrenheit. Lightly grease a 9 x 13 inch baking pan with vegetable oil. Line with parchment paper and lightly grease again.Make the parchment paper long enough so there is about a ½ inch overhang on each side so that you can lift the cake out easily once it has cooled.
In a large bowl, whisk together the 1 ¼ cups of gluten free flour, the ¼ cup cocoa powder, the ½ cup granulated sugar, the 2.5 teaspoons of baking powder and the ½ teaspoon kosher salt. Set aside.
In a large bowl, using a spoon, mix together the 2 heaping tablespoons cornstarch (26 grams) and the 3 tablespoons water until thin and watery. It will be thick and tacky at first.
Into the cornstarch water, whisk in the ¾ cup of milk, the 2 tablespoons vegetable oil and the 2 teaspoons pure vanilla extract until combined.
Pour the dry ingredients into the wet a little bit at a time. Once the batter gets too thick to whisk, switch to using a spatula.
Spoon the batter into your parchment lined and greased 9 x 13 baking dish and use a spatula to press the batter down into the shape of the pan. Then use a butter knife or a small icing spatula to spread the batter around. The batter will be super sticky and may stick to the parchment or the icing spatula. Rinse the icing spatula and then shake off any excess water. You want it slightly wet but not dripping wet. This will help prevent the dough from sticking. You may need to repeat this a few times. It might appear as though there isn’t enough batter, but it’s fine. You just need to really spread it out. Just be patient. You should end up with a smooth even thin layer of batter.
Cut the 1 cup of unsalted butter into pieces and place them a heat safe bowl. Microwave in 20 second increments, stirring after each time until melted. Set aside and let cool.
In a medium bowl, whisk together the 2.5 cups gluten free flour for the crumb topping, the 5 tablespoons cocoa powders for the crumb topping, the 1 cup light brown sugar and the 1.5 teaspoons ground cinnamon. After it's all combined, pour in the melted butter and stir with a spatula until large crumbs form.
Sprinkle the crumbs all over the batter. There are lots of crumbs...make sure to use them all and cover every inch of batter.The crumbs will end up going on top of one another. That's normal.
Bake the cake in the center rack of the oven at 325 degrees Fahrenheit for 30 minutes. Let the cake cool almost completely in the pan before trying to remove it, otherwise it will break apart into a giant mess.
After the chocolate cake is cool, use the parchment overhang to lift onto a cooling rack and let it cool completely before adding the sugar otherwise the sugar will melt.Dust the entire cake with confectioners' sugar and then slice the chocolate crumble cake into big squares, tiny squares, large rectangles or small rectangles...whatever you prefer! I slice mine into 16 squares.
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Notes
Vegan: Use a dairy free gluten free flour, vegan sugar, vegan baking sticks and non dairy milk.All Purpose Flour: I cannot test this due to celiac disease, but use 1 ¼ cups packed cups of AP flour (210 grams) in the cake and 2 ½ packed cubs for the crumbs (420 grams). For the coca powder, use 4 packed tablespoons of cocoa powder (29 grams) in the cake and 5 packed tablespoons (36.25 grams) in the crumbs. Storing: Cut the entire cake into squares. Store the extra squares individually wrapped in foil (do not put them in an airtight container because it makes the bottoms of the chocolate cake squares get very wet) and then pop them in a zip top bag at room temperature for up to 3 days or in the freezer for 30 days. If in the freezer, let come to room temperature prior to eating. Nutrition: The info below is a generated estimate and is not guaranteed to be accurate.