For the Cake
- 2 1/2 cups all-purpose gluten-free flour
- 1 teaspoon xanthan gum
- 1 teaspoon baking powder
- 1/2 teaspoon baking soda
- 1 teaspoon ground cinnamon
- 1/2 teaspoon salt
- 1 cup granulated sugar
- 1/2 cup unsalted butter, at room temperature
- 1 heaping tablespoon lemon zest
- 2 teaspoons pure vanilla extract
- 3 tablespoons pure maple syrup, plus 3 tablespoons more for topping
- 2 large eggs
- 1 1/2 cups buttermilk
- 1 cup fresh blueberries
For the Topping
- 1/2 cup all-purpose gluten-free flour
- 3 tablespoons unsalted butter, cold and cut into cubes
- 3 tablespoons granulated sugar
- 3 tablespoons old-fashioned oats
- 1/2 teaspoon ground cinnamon
- 1/2 teaspoon ground nutmeg
- pinch of salt
- Place a rack in the upper third of the oven and preheat oven to 350 degrees F. Grease and flour a 9-inch square baking pan and set aside.
- In a medium bowl, whisk together flour, xanthan gum, baking powder, baking soda, cinnamon, and salt. Set aside.
- In the bowl of an electric stand mixer fitted with a paddle attachment (or you could use a large bowl and a set of hand beaters) beat together sugar, butter, and lemon zest until light and fluffy, about 3 to 5 minutes. Beat in the vanilla extract and maple syrup.
- Beat in the eggs, one egg at a time, beating for 1 minute between each addition.
- Stop the mixer and remove the bowl from the stand. Add the dry ingredients, all at once, to the butter mixture. Use a rubber spatula to fold a few strokes. Add the buttermilk and fold until just combined. Be sure to scrape the bottom of the bowl well to evenly mix the batter.
- Add the blueberries (reserving a small handful for topping) and fold to combine.
- Spoon the batter into the prepared pan and smooth the top with a spatula. Sprinkle on the remaining blueberries
- To make the crumble, in a small bowl combine all of the ingredients and use your fingers to break up the bitter bits into the mixture. Some of the butter will be the size of small peas, others the size of oat flakes.
- Sprinkle the topping over the cake and place in the oven. Bake for 40 to 45 minutes or until a skewer inserted in the center of the cake comes out clean or with just a few moist crumbs. Allow the cake to cool for 30 minutes before serving.
- Drizzle with maple syrup before serving.
- Cake will last, well wrapped at room temperature, for 3 days.