Preheat oven to 250°.
Cover a baking sheet with parchment paper; secure with masking tape.
Place egg whites, cream of tartar, and salt in a large bowl; beat with a mixer at high speed until foamy. Combine sugar and 3 tablespoons cocoa, stirring with a whisk. Gradually add sugar mixture to egg white mixture, 1 tablespoon at a time, beating at medium speed until stiff peaks form. Gently fold in minichips and vanilla.
Spoon mixture into a pastry bag fitted with a 1/2-inch round tip, or large zip-top plastic bag with 1 corner snipped to form 1/2-inch opening. Pipe 30 (2-inch-round) mounds 1/4 inch apart onto prepared baking sheet. Bake at 250° for 1 1/2 hours.
Turn oven off; cool meringues in closed oven for 1 hour. Carefully remove meringues from paper. Using a fine sieve, dust meringues with 1 tablespoon cocoa.