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1
Line 9- by 13-inch pan with parchment paper, allowing paper to overhang the sides. Press ice cream into pan and smooth top. Freeze until solid, at least one hour.
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2
Adjust oven rack to upper-middle and lower-middle position and preheat oven to 350°F. Line 2 baking sheets with parchment paper. Sift flour, cocoa, and salt into medium bowl; set aside.
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3
In bowl of standing mixer fitted with paddle attachment, cream sugar with butter on medium speed until combined and slightly lightened, about 1 minute. Mix in yolks and then vanilla. Mix in dry mixture until just combined. Divide dough into 2 pieces and pat each piece into a 5-inch square, wrap with plastic wrap, and chill until firm, about 30 minutes.
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4
On a lightly floured surface and working with one piece of dough at a time, roll dough into an 8-inch by 12-inch rectangle. Along the long side, use ruler to cut into 2-inch lengths (you should have 6 pieces). Cut each length in half, creating 12 4x2-inch cookies. Use flat spatula to place cookies onto prepared pans. Using the pointy tip of a thermometer, poke about 15 holes into cookies. Bake until cookies are firm, about 10-12 minutes, rotating pans from top to bottom and front to back halfway through baking. Cool completely.
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5
Remove ice cream from pan and trim the edges to make a neat rectangle. Using the same technique as with the dough, cut the ice cream into 12 4 by 2-inch rectangles. Sandwich the ice cream with the cookies. Wrap the assembled sandwiches separately in parchment paper or foil, and store overnight or serve immediately.
