PREHEAT THE OVEN AND PREPARE THE PAN

1. Preheat the oven to 350°F (177°C).
2. Grease and flour a 9-inch springform pan and line the bottom with parchment paper. Set aside.

MAKE THE STREUSEL

1. In a medium bowl, whisk together the gluten-free 1:1 flour, almond flour, granulated sugar, brown sugar, and salt.
2. Pour in the melted butter and vanilla extract and stir until the mixture forms moist crumbs.
3. Add the oats and sliced almonds and mix until evenly incorporated. Refrigerate while preparing the cake batter.

PREPARE THE CAKE BATTER

1. Reserve 1 tablespoon of the gluten-free 1:1 flour for the blueberries. In a medium bowl, whisk together the remaining gluten-free flour, almond flour, baking powder, baking soda, and salt. Set aside.
2. In a large mixing bowl, beat the butter and sugar together on medium-high speed for about 3 minutes, until light and fluffy.
3. Add the eggs, one at a time, mixing well after each addition until fully incorporated.
4. With the mixer on low speed, slowly stream in the oil and mix until combined.
5. Add the sour cream, vanilla extract, and almond extract, and mix on low speed until smooth and fully incorporated.
6. Add half of the dry ingredients to the wet ingredients and mix on low speed until just combined. Add the remaining dry ingredients and continue mixing on low speed until just combined, being careful not to overmix.
7. Toss the blueberries with the reserved tablespoon of flour, then gently fold them into the batter using a rubber spatula until evenly distributed.

BAKE THE CAKE

1. Pour the batter into the prepared pan and smooth into an even layer. Sprinkle the streusel evenly over the top.
2. Bake for 50–60 minutes on the center rack, tenting loosely with foil halfway through if the streusel begins to brown too quickly. The cake is done when a toothpick inserted into the center comes out clean or with a few moist crumbs.
3. Allow the cake to cool in the pan for 1 hour before releasing the sides.

MAKE THE LEMON GLAZE

1. In a small bowl, whisk together the powdered sugar, lemon juice, and 1 teaspoon of half-and-half or milk.
2. Add more liquid, 1 teaspoon at a time, until the desired consistency is reached.
3. Drizzle the glaze over the cooled cake, slice, and serve.

Store the cake loosely covered at room temperature for 2 days or covered in the refrigerator for up to four days. Allow refrigerated slices to come to room temperature before serving for the best texture.