1. Preheat oven to 225°.
2. Cover a large baking sheet with parchment paper. Draw 6 (3-inch) circles on paper. Turn paper over; secure with masking tape.
3. Place egg whites, vanilla, and cream of tartar in a large bowl; beat with a mixer at high speed until foamy. Gradually add 1/2 cup sugar, 1 tablespoon at a time, beating mixture until stiff peaks form. Gently fold in cocoa.
4. Divide egg white mixture evenly among the 6 drawn circles. Shape meringues into nests with 1-inch sides using the back of a spoon.
5. Bake at 225° for 1 1/2 hours or until dry. Turn oven off, and cool meringues in closed oven at least 12 hours. Remove from oven; carefully remove meringues from paper.
6. Place meringues on individual dessert plates. Top each with 1/3 cup ice cream. Sprinkle each evenly with 1 1/2 tablespoons cookie crumbs and 1 teaspoon pecans; drizzle each sundae with 1 1/2 teaspoons chocolate syrup. Serve immediately.