In a mixing bowl, combine the hot melted butter and sugar and stir to dissolve the sugar. Add the vanilla extract, egg, buttermilk, and oil and stir to combine.
In a separate mixing bowl, whisk together the flour, cocoa powder, baking powder, baking soda, and salt. Form a well in the center and pour in the wet ingredients, then gently fold together until no raw flour remains visible. Gently fold in the chocolate chips.
Preheat oven to 350℉. Lightly grease both the cupcake tin and cupcake wrappers with nonstick spray. Use a spoon or scoop to fill each wrapper three-quarters full with batter. Sprinkle the cupcakes with a dusting of demerara sugar (optional) and bake for 15-17 minutes, until a toothpick inserted in the center comes out with a few wet crumbs attached.
Allow the cupcake tin to cool for 5 minutes before turning out onto a wire rack, then turn the cupcakes out of the tin. Decorate as desired.
