In saute pan, heat butter over medium-low heat until softened. Remove from heat, add cookie crumbs to pan and stir until butter is evenly distributed through the crumbs.
Line a "half sheet" size pan (approximately 13 by 18 by 2 inches deep) with plastic wrap. Spread half the cookie crumb mixture over the plastic.
With a mixer on lowest speed (or by hand), combine ice cream and mint candy, mixing slowly and trying to avoid breaking up the mints.
Pour the ice cream mixture over the cookie crumbs and spread gently throughout the pan, trying not to break the cookie crumb base. Top evenly with remaining cookie crumb mixture, cover with plastic wrap and re-freeze for a few hours.
Cut into 12 triangular pieces, by cutting in half lengthwise, then thirds crosswise, and cutting each resulting rectangle into right triangles. Serve each triangle topped with whipped cream, chocolate syrup, and mint sprigs.