Cupcakes:
2 large egg yolks, at room temperature
1/4 cup vegetable oil
2/3 cup sugar
2 tablespoons unsweetened cocoa powder
1 teaspoon pure vanilla extract
1/2 teaspoon ground cinnamon
1/8 teaspoon fine sea salt
1/2 cup semisweet chocolate chips, melted
1/4 cup cake flour
3 large egg whites, at room temperature

Topping:
1 cup semisweet chocolate chips, melted
1 tablespoon vegetable oil

Special equipment: a (24-count) mini-muffin pan, 18 to 20 (1.25-inch diameter)
paper mini-muffin cup liners, recommended: Wilton