Slice 1 inch off one end of each sandwich cookie. Pulse these trimmed pieces in a food processor with almonds until crumbs are formed and almonds are ground. Add softened butter and pulse until evenly combined. Press crumbs onto the bottom of a 9-inch pie plate, covering your hand with plastic wrap to avoid sticking. Prop remaining cookies, cut side down, around rim of plate. Refrigerate until ready to fill.
Let mascarpone cheese soften in a large bowl at room temperature. Beat slightly with a hand mixer until smooth. Meanwhile, sprinkle gelatin over 1/4 cup cold water in a 1-cup glass measuring cup. Let soften 2 minutes, then microwave for 15 seconds, until gelatin is dissolved. Let cool slightly.
Gradually beat creme de menthe syrup and sugar into mascarpone until blended; mixture will look curdled. While mixer is running, add 1-1/4 cups of the heavy cream. Beat until soft peaks are formed. Gradually beat in gelatin; beat until medium-stiff peaks are formed. Pour into prepared crust, swirling top decoratively. Refrigerate 4 hours or until set.
Once pie is set, beat remaining 1/3 cup cream to soft peaks. Dollop on top of pie and sprinkle with chocolate curls and mint sprigs. Makes 12 servings.