Prep your pan and oven. Preheat oven to 350°F (175°C). Line an 8-inch square pan or 9-inch round pan with parchment, leaving some overhang for easy lifting. Grease lightly.

Mix the dry ingredients. In a large bowl, whisk almond flour, coconut flour, 1/2 cup sweetener, baking powder, 1/2 teaspoon cinnamon, and salt. Break up any clumps for a smooth batter.

Whisk the wet ingredients. In a separate bowl, whisk eggs, almond milk, melted butter (4 tablespoons for the batter), vanilla, and sour cream until smooth.

Combine to make the batter. Pour the wet ingredients into the dry. Stir until just combined. The batter should be thick but spreadable. If it seems too stiff, add 1–2 tablespoons more almond milk.

Make the cinnamon crumble. In a small bowl, mix 2 tablespoons sweetener, 2 teaspoons cinnamon, and a pinch of salt. Stir in 2 tablespoons melted butter until clumpy and sandy.

Layer and top. Spread the batter evenly in the pan. Sprinkle the crumble over the top, covering the surface as evenly as possible without pressing it down.

Bake. Bake for 25–32 minutes, until the edges are set and a toothpick in the center comes out mostly clean with a few moist crumbs. Do not overbake—almond flour browns quickly.

Cool. Let the cake cool in the pan for 15 minutes, then lift it out using the parchment and cool to room temperature on a rack. This helps it set and slice cleanly.

Add the optional glaze. Whisk powdered sweetener, almond milk, and vanilla until smooth. Drizzle over the cooled cake in thin lines.

Slice and serve. Cut into 9–12 squares. Enjoy warm or at room temperature with coffee or tea.