S'mores Brownie Cupcakes

Name: S'mores Brownie Cupcakes
Prep time: 30 min
Cook time: 25 min
Total time: 55 min
Cuisine: American
Ingredients: 1 and 1/2 cups (180g) graham cracker crumbs (about 12 full-sheet graham crackers); 1/4 cup (50g) granulated sugar; 6 Tablespoons (85g) unsalted butter, melted; 1/2 cup (8 Tbsp; 113g) unsalted butter; 2 4-ounce quality semi-sweet chocolate bars (228g), coarsely chopped; 1 cup (200g) granulated sugar; 3 large eggs, at room temperature; 1 teaspoon pure vanilla extract; 1/2 cup (63g) all-purpose flour (spooned & leveled); 1/4 cup (21g) unsweetened natural or dutch-process cocoa powder; 1/2 teaspoon salt; 3 large egg whites, at room temperature; 3/4 cup (150g) granulated sugar; 1/8 teaspoon cream of tartar (do not skip!)