Preheat oven to 180 degrees Celsius. Line 2 baking sheets with parchment paper.
In a bowl, sift together flour, cornstarch, cocoa powder and salt.
In another bowl, beat butter and confectioner’s sugar till light and fluffy, 5 to 7 minutes, scrapping the sides occasionally. Add flour mixture, mixing, until smooth. Stir in chocolate chips.
Scoop cookie batter by heaping teaspoonfuls, drop them onto prepared baking sheets. Bake for 10 to 12 minutes till firm around the edges. Remove to wire rack and generously sprinkle hot cookies with extra confectioner’s sugar. Let cookies cool completely on baking sheets on racks.
NOTES
These cookies can be kept in an airtight container for up to 14 days.