Prep the pan: Heat oven to 350°F (175°C). Grease an 8-inch square pan and line with a parchment sling for easy removal.

Melt butter and chocolate: In a small saucepan over low heat, melt the butter with the chopped chocolate, stirring until smooth. Set aside to cool slightly for 5 minutes.

Whisk wet ingredients: In a medium bowl, whisk the granulated sugar, brown sugar, eggs, and vanilla until glossy and slightly thick, about 30 seconds. Whisk in the sour cream until smooth.

Combine chocolate mixture: Slowly whisk the melted chocolate-butter into the egg mixture until fully blended.

Mix dry ingredients: In another bowl, whisk almond flour, all-purpose flour, cocoa, baking powder, baking soda, and salt to break up any clumps.

Bring it together: Add the dry ingredients to the wet and stir with a spatula just until you no longer see streaks of flour. If the batter feels very thick, fold in 1–2 tablespoons milk or hot coffee. Fold in sliced almonds.

Pan and top: Spread batter into the pan, smoothing the top. Sprinkle a handful of sliced almonds over the surface for crunch.

Bake: Bake 22–28 minutes, until the center is just set and a toothpick comes out with a few moist crumbs. Don’t overbake—this cake is best a touch fudgy.

Cool and slice: Let the cake cool in the pan for 15 minutes, then lift out using the parchment. Cool to warm or room temperature before slicing into squares.

Finish (optional): Dust with powdered sugar, drizzle with a little melted chocolate, or serve with berries and a spoonful of yogurt or whipped cream.