Step 1

1 Make the crust: In the bowl of a stand mixer fitted with the paddle attachment — or, if using a hand mixer, in a large bowl — beat together the butter and cream cheese until smooth, about 2 minutes

Step 2

2 Stop the mixer and add the flour

Step 3

3 On low speed, mix until no streaks remain and the dough starts to come together, about 1 minute

Step 4

4 Scrape any stray dough from the sides of the bowl, gather into a ball and flatten into a smooth rectangle or disc

Step 5

5 Cover tightly and refrigerate for 1 hour

Step 6

6 Cut the cold dough into 12 equal pieces, about 1-inch cubes, and, using your fingers, evenly press each piece into the bottom and up the sides of 12 mini muffin cups, making sure there are no holes

Step 7

7 Refrigerate, uncovered, while you make the filling

Step 8

8 Position a rack in the middle of the oven and preheat to 350 degrees

Step 9

9 Make the filling: Place the cocoa powder in a small, heatproof bowl

Step 10

10 In a small skillet over medium-high heat, heat the butter just until it’s melted

Step 11

11 Immediately pour it over the cocoa, and stir until smooth

Step 12

12 Stir in the sugar, flour, egg white and salt just until combined

Step 13

13 Stir in the chopped chocolate until the mixture is combined, but still chunky

Step 14

14 Retrieve the muffin pan from the refrigerator, and using a soup spoon, fill each dough cup about 3/4 of the way

Step 15

15 Bake for 15 to 20 minutes, or until the crust is golden brown and the filling is puffed and set

Step 16

16 Transfer the pan to a wire rack and let cool completely before removing the tassies

Step 17

17 Top each with a pinch of flaky sea salt, if desired, before serving

Step 18

18 NOTE: If doubling this recipe, you can use 2 egg whites or 1 whole egg