Ganache: Heat the heavy cream until it just begins to bubble, stirring constantly. Pour over the chocolate chips and stir until smooth. Cover and freeze until solid, about 30 minutes. Keep frozen until ready to use.
60 g heavy cream, 100 g semi-sweet chocolate chips
Cream the butter, brown sugar, and granulated sugar until light and fluffy.
227 g unsalted butter, 213 g brown sugar, 100 g granulated sugar
In a separate bowl, mix the dry ingredients.
300 g all-purpose flour, 50 g cocoa powder, 1 tsp salt, 1 tsp baking soda, 1½ tsp espresso powder
Mix in the vanilla and egg until just combined. Add the dry ingredients and mix, then stir in the mini chocolate chips. The dough will be thick.
Preheat the oven to 350°F. Scoop a 2-tablespoon ball of dough, flatten it, place ½ teaspoon frozen ganache in the center, fold the dough around it, and roll into a smooth ball.
Roll each ball in the sugar (and cardamom, if using) and place 2 inches apart on a lined sheet.
⅓ cup granulated sugar, ½ tsp cardamom
Bake 13–15 minutes (14 is the sweet spot), keeping the ganache frozen between batches. Cool on the pan 5 minutes before transferring.
Notes
The cookies are done when the tops are no longer shiny — don't overbake.
Let them cool on the pan a few minutes so the bottoms set and support the gooey ganache center.
Use 1–1½ cups mini chocolate chips in the dough (a 12-oz bag is ~1½ cups).
Store at room temperature for up to 7 days, or freeze for up to 6 months (thaw in the fridge).