Use a fork to mix together the chocolate wafer crumbs and butter. Spray the cups of a 6-muffin tin with a vegetable spray. Line the cups with strips of parchment or waxed paper, cut so that they are as wide as the diameter of each cup and long enough to overhang the sides (you’ll need this overhang to remove the tarts). Use the bottom of a small glass to press the crumbs over the bottom and sides of the muffin cups, building the sides up to only about 1 1/2 inches. Place a raspberry in the center of each crust and with a pastry bag or small plastic bag with the corner snipped off, fill the tarts with the truffle mixture. Smooth the tops and refrigerate until set, about 2 hours.