Heat the oven: Preheat to 350°F (175°C). Line an 8-inch square pan with parchment, leaving overhang for easy lifting.
Lightly grease the sides.
Mix dry ingredients: In a large bowl, whisk all-purpose flour, almond flour, cocoa, baking powder, baking soda, and salt until evenly combined.
Whisk wet ingredients: In a separate bowl, whisk eggs, brown sugar, and granulated sugar until smooth. Add yogurt, oil, and vanilla. Whisk until glossy.
Combine: Pour the wet mixture into the dry and stir until just combined.
The batter will be thick.
Loosen with heat: Stream in the hot coffee (or water) and whisk gently until smooth. Fold in the dark chocolate chips.
Top and bake: Pour batter into the pan. Scatter toasted sliced almonds over the top.
Bake 24–30 minutes, or until a toothpick comes out with a few moist crumbs.
Cool: Let the cake cool in the pan for 15 minutes, then lift out and finish cooling on a rack. Sprinkle with flaky sea salt if you like.
Serve: Cut into squares. Enjoy slightly warm or at room temperature.