How to Make It
In a food processor, pulse the chocolate until it is the size of peas. Transfer to a plate and freeze for 30 minutes.
Preheat the oven to 325°. Line 2 rimmed baking sheets with parchment paper. Sift both flours with the cocoa powder, baking soda and salt. In a large bowl, using an electric mixer, beat the butter with both sugars at medium speed until very light and fluffy, 5 minutes. Beat in the flour mixture just until incorporated, then stir in the frozen chocolate.
Drop almond-size clumps of the dough in a single layer onto the prepared baking sheets; the dough will look crumbly and uneven. Bake for 8 to 10 minutes, until the top is dry but the crumble is still soft. Let cool completely. Serve over ice cream.