Preheat oven to 350F and line 2 sheet pans with parchment
1. Melt butter and chocolate in a double boiler over simmering water. Stir until smooth, then set aside to cool.
2. Sift pr stir together flour and baking powder, then add salt.
3. Whip the eggs, sugar, and vanilla extract together until thick. Then gently stir in the cooled chocolate mixture. Stir in the flour mixture and let the batter rest until it thickens slightly. (It will go from brownie batter-y to ganache-y. I scooped mine slightly before it hit the ganache phase, see picture.) This could take anywhere from 5 -15 minutes, depending on the temperature of your chocolate when you added it to the eggs.
4. Scoop by large tablespoonfuls onto parchment and flatten slightly with your finger or the back of your scoop. You should end up with about 20 cookies.
5. Bake for about 10 minutes until they’re no longer shiny and they begin to crack. Cool FOR A LONG TIME VERY PATIENTLY on a cooling rack.
6. When you’re ready to assemble your ice cream cookies, set your ice cream out for about 10 minutes to soften, then put a scoop on each of 10 cookies, and top each scoop with another cookie. Freeze in a single layer for about 20 minutes, then wrap in plastic wrap and store in a ziploc bag for future enjoyment.