Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.

In a bowl, whisk together flour, cocoa powder, baking powder, and salt.

In another bowl, cream the butter and sugar until light and fluffy. Add the egg and vanilla extract, mixing well.

Gradually add the dry ingredients to the wet ingredients, mixing until a dough forms.

Roll out the dough into a rectangle on a lightly floured surface.

Melt the chocolate chips and heavy cream together to create the filling. Spread the filling evenly over the dough.

Roll the dough tightly into a log and refrigerate for 30 minutes to firm up.

Slice the log into 1/2-inch thick cookies and place them on the prepared baking sheet.