0.3 cup cocoa powder unsweetened (preferably Dutch-process)
1 teaspoon vanilla extract
6 servings chocolate white chopped (such as Lindt or Baker's)
Equipment
bowl
baking sheet
sauce pan
baking paper
oven
spatula
Directions
Drop six 2/3-cup mounds mint chocolate chip ice cream onto waxed-paper-lined baking sheet. Using metal spatula, shape each mound into 3- to 3 1/2-inch square; freeze squares.
Beat butter and sugar in large bowl until smooth. Beat in egg yolk and vanilla. Sift flour, cocoa and salt onto butter mixture. Stir until blended and soft dough forms. Gather dough into ball; flatten into rectangle.
Roll out dough between 2 sheets of waxed paper to 13 x 10-inch rectangle.
Place dough, still between waxed paper sheets, on baking sheet. Chill until firm, at least 1 hour and up to 1 day.
Position rack in center of oven and preheat to 300°F. Line large baking sheet with parchment paper. Peel top sheet of waxed paper off dough. Trim dough to 12 x 9-inch rectangle; cut dough into twelve 3-inch squares.
Transfer squares to parchment-lined sheet, discarding waxed paper and spacing squares about 1 inch apart.
Bake until cookies are firm to touch, about 20 minutes. Cool cookies completely on sheet.
Melt white chocolate in medium metal bowl set over saucepan of barely simmering water, stirring until smooth (do not allow bottom of bowl to touch water).
Remove bowl from over water.
Holding corner of 1 cookie, dip cookie into melted chocolate until half covered on diagonal, tilting bowl if necessary to submerge. Shake cookie gently to allow some excess chocolate to drip back into bowl. Return dipped cookie to parchment-lined baking sheet. Repeat with remaining cookies and white chocolate. Freeze cookies until chocolate coating is firm, about 10 minutes.
Arrange 6 cookies, flat side up, on work surface. Top each with frozen ice cream square, then another cookie, flat side down, pressing slightly to adhere. Cover and freeze sandwiches. (Can be made 4 days ahead. Keep frozen.)
