Prep your pan and oven. Heat the oven to 350°F (175°C). Line an 8-inch square pan or 9-inch round pan with parchment and lightly grease the sides. This helps the cake release cleanly and prevents over-browning.

Whisk the dry ingredients. In a large bowl, combine 1 1/2 cups almond flour, 1/2 cup whey or whey-casein protein powder, 1/2 cup oat flour, 1 1/2 teaspoons baking powder, 1/4 teaspoon baking soda, and 1/4 teaspoon salt. Break up any clumps with a whisk for an even crumb.

Mix the wets. In another bowl, whisk 3/4 cup Greek yogurt, 2 large eggs, 1/3 cup almond milk, 1/4 cup avocado oil, 1/3 cup maple syrup, 1 1/2 teaspoons vanilla extract, and 1/4 teaspoon almond extract. Stir in 1 teaspoon lemon zest if you like a citrus lift.

Combine gently. Pour the wet mixture into the dry bowl. Stir with a spatula just until no dry pockets remain. The batter should be thick but scoopable. Avoid overmixing to keep the cake tender.

Fold in the blueberries. Toss 1 to 1 1/4 cups blueberries with 1 teaspoon oat flour to prevent sinking. Fold into the batter with a few gentle strokes. If using frozen berries, add straight from the freezer.

Pan and top. Spread the batter into the prepared pan. Smooth the top, then sprinkle with 2 to 3 tablespoons sliced almonds. For a pastry-style finish, lightly press a few extra blueberries into the surface.

Bake. Bake for 28–35 minutes, or until the top is golden and a toothpick inserted in the center comes out mostly clean with a few moist crumbs. If using a glass pan, start checking at 30 minutes.

Cool the cake. Let it cool in the pan for 10 minutes, then lift out using the parchment and cool fully on a rack. This helps the structure set and keeps slices clean.

Finish and serve. Dust lightly with your preferred sweetener or a pinch of powdered sugar if desired. Slice into 9 or 12 pieces. Serve plain, or with a spoonful of Greek yogurt and a few fresh berries.