Chocolate-Pistachio Tartufo

Line a small domed glass bowl (ours was 4 1/2-inch-diameter with a 1 1/3-cup capacity) with plastic wrap, leaving a 4-inch overhang on all sides. Pack 1 ice cream flavor into each side of bowl. Make an indentation in each flavor; place a cherry in each and cover with ice cream. Wrap in plastic and freeze until firm, at least 2 hours and preferably overnight.

In a bowl, mix together cookie crumbs and 1 teaspoon oil. Fold back plastic and press crumb mixture onto ice cream; smooth with an offset spatula. Rewrap and freeze at least 15 minutes.

Place chocolate in a heatproof bowl set over (not in) a pan of simmering water. Stir until melted. Remove from heat; stir in remaining 1 1/2 teaspoons oil.

Fold back plastic from ice cream. Invert bowl onto a wire rack set over a baking sheet. With a hot cloth, wipe outside of bowl to loosen. Lift bowl and completely remove plastic. Pour chocolate over top, starting in center and working outward, in one stream.

Freeze tartufo on rack to harden, at least 5 minutes. Serve, or wrap loosely in plastic and keep frozen up to a week. To serve, transfer to a plate with a thin metal spatula (if it sticks, dip spatula in hot water and wipe dry).