-
1
Sift flour, cocoa powder, baking powder, and salt into a large bowl.
-
2
Put butter and sugar in the bowl of an electric mixer fitted with the paddle attachment; mix on medium speed until creamy.
-
3
Mix in egg and vanilla.
-
4
Reduce speed to low.
-
5
Add flour mixture; mix until just combined.
-
6
Halve dough, and wrap in plastic.
-
7
Refrigerate about 1 hour.
-
8
Roll dough on a lightly floured surface to 1/8 inch thick.
-
9
Cut into 1 1/2-inch squares.
-
10
Space 1 inch apart on baking sheets lined with parchment paper.
-
11
Refrigerate 30 minutes.
-
12
Wrap scraps in plastic, and refrigerate 30 minutes; reroll and cut.
-
13
Preheat oven to 325F.
-
14
Bake cookies until edges just begin to brown, about 12 minutes, rotating halfway through.
-
15
Cool on sheets on wire racks.
-
16
Put 9 ounces chopped white chocolate in a bowl.
-
17
Bring cream to a boil.
-
18
Pour over chocolate; let stand 5 minutes.
-
19
Stir until smooth.
-
20
Chill until spreadable, about 1 hour, stirring occasionally.
-
21
Spread onto bottom of half the cookies.
-
22
Sandwich with remaining cookies.
-
23
Melt remaining chocolate in a small heatproof bowl set over a pan of simmering water.
-
24
Fill a parchment paper cone, or a small pastry bag fitted with a round tip (such as Ateco #2), with melted chocolate; decorate cookies.
-
25
Cookies can be refrigerated in airtight containers up to 1 week.
