Stir together flour, cocoa, salt and baking powder in a bowl. Set aside

Beat beat butter, sugar and espresso in a stand mixer with paddle attachment on medium until light and fluffy, approx 4min

With mixer running, add egg. Beat until well combined. Stir in vanilla. Gradually add flour mixture, beating on low speed until combined, approx 30sec

Wrap dough in plastic wrap and chill until firm, at least 2hr and up to 3 days

Preheat oven to 350°F

Roll dough out on parchment paper line work surface into a large (14x11in) rectangle, approc 1/8in thick. Flour top of dough as needed to prevent sticking

Trim to 13x10in rectangle. Slide parchment paper with dough onto baking sheet. Chill until firm, approx 30min

Using blunt end of a wooden skewer, poke holes in dough approx 3/4in apart

Bake until set in middle but still soft, approx 9-11min

Transfer to wire rack. Cool completely, approx 30min

Cut cookie crosswise into 2 rectangles. Invert 1 half onto aluminum foil

Top half with ice cream, spreading to edges in an even layer. Place remaining cookie half on top

Wrap in aluminum foil and freeze 8hr

Remove from foil and trim edges. Cut into 12 bars

Serve immediately