In food processor, finely grind cookies; pulse in butter and 1/4 cup sugar. Press into 9-inch pie dish. Bake at 350° until firm, about 10 minutes; let cool. In pot, cook cherries and remaining 1/4 cup sugar over medium heat, stirring often, until syrupy, about 15 minutes. Stir in liqueur; chill. Spread half of cherry mixture in crust; top with ice cream. Freeze for 3 hours. Serve with remaining cherry mixture.