Heat the oven to 350 degrees.

Place the chocolate in the top of a double boiler or a heatproof bowl set over simmering water or in a small metal bowl over simmering water. Stir the chocolate occasionally until it is melted, about 5 minutes. Remove from heat and reserve.

In a small bowl, sift together the flour, cocoa, and salt. In the bowl of an electric mixer fitted with a paddle attachment, beat the butter and sugar together until it resembles coarse meal. Add the eggs one at a time, beating well after each addition. Beat for another 3 to 4 minutes, until pale and creamy.

Add the melted chocolate and vanilla and beat until combined, scraping the bottom of the bowl once or twice. On low speed, add the flour mixture and then stir in the white chocolate chips. Spray a nonstick pan lightly with cooking spray. Scoop the cookies with a 11/2- inch cookie scoop or 1/4 cup measuring cup and leave 2 to 3 inches between them on a baking sheet.

Bake for 15 minutes until cookies are cracked on top and still a little soft. Let cool for 3 to 4 minutes, then transfer the cookies from the sheet pan to a cooling rack.

When the cookies are completely cool, place them in a single layer on a paper plate and freeze them overnight, or up to a week, covered tightly in plastic.

Place 1/4 cup slightly softened ice cream on top of 10 of the cookies and top each scoop with another cookie, pressing down slightly. Cover with plastic and freeze until completely firm, at least 4 hours and up to 3 days.