Preheat and prep the pan. Heat your oven to 350°F (175°C). Line an 8x8-inch square pan with parchment paper, leaving overhang for easy lifting. Lightly grease the sides.

Mix the dry ingredients. In a large bowl, whisk 2 cups almond flour, 2 tablespoons coconut flour, 2 teaspoons baking powder, and 1/4 teaspoon salt until smooth and lump-free.

Whisk the wet ingredients. In another bowl, whisk 3 large eggs, 1/2 cup granular keto sweetener, 1/2 cup sour cream, 1/3 cup melted butter (slightly cooled), and 2 teaspoons vanilla. If the mixture looks very thick, add 1–2 tablespoons unsweetened almond milk.

Combine to make the batter. Stir the wet mixture into the dry ingredients until just combined. The batter should be thick but scoopable. If it’s too stiff, add another tablespoon of almond milk.

Make the cinnamon swirl. In a small bowl, mix 1/3 cup brown-style keto sweetener, 1–1.5 tablespoons ground cinnamon, and 2 tablespoons melted butter until you get a thick, sandy paste.

Layer the cake. Spread half the batter in the pan. Dollop half the cinnamon mixture over the batter in small spoonfuls. Swirl gently with a knife. Repeat with the remaining batter and cinnamon mixture, then swirl again lightly. Don’t overmix or you’ll lose the ribbon effect.

Bake. Bake for 28–35 minutes, until the top is golden and a toothpick comes out mostly clean with a few moist crumbs. Do not overbake—almond flour dries out if baked too long.

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

Optional glaze. Mix 1/2 cup powdered keto sweetener with 1–2 tablespoons almond milk and 1/4 teaspoon vanilla until smooth. Drizzle over the cooled cake.

Slice and serve. Cut into 9 generous squares or 12 smaller pieces. Enjoy with coffee or tea.