Make tart shells: Place cookies in food processor and pulse to form fine crumbs. Add melted butter and pulse until evenly coated; mixture should hold together when squeezed. Divide mixture among tart pans and press firmly and evenly into corners, up sides and on bottom. Refrigerate at least 10 minutes.
Make filling: Place chocolate in medium bowl. In small saucepan, heat cream on medium until small bubbles form around sides of pan. Pour cream over chocolate and let sit 1 minute. Stir until chocolate is fully melted, then add butter, stirring until melted. If using, spoon 1 tablespoon caramel into each tart shell. Divide chocolate mixture among shells (scant ⅓ cup each) and refrigerate at least 1 hour, until ready to serve.
Make meringue ghosts: Fill medium saucepan with 1 inch water and bring to a boil. To large bowl, add egg whites, sugar, ¼ cup water and cream of tartar. Place bowl over saucepan (making sure bottom doesn’t touch water). Using electric mixer, beat mixture until stiff peaks form, about 5 minutes. Remove from heat and continue beating until mixture cools, about 2 minutes.
Spoon small mounds of meringue onto tarts and drag spoon through mixture to make a swoop. Add mini chocolate chips for eyes and serve immediately with extra meringue. Remove from pans just before serving.
