Preheat oven to 350°F (175°C). Line cupcake pans with liners (about 30).

In a large mixing bowl, whisk together the flour, granulated sugar, cocoa powder, baking soda, and salt.

In a separate large cup or bowl, combine the hot water, vegetable oil, white vinegar, instant coffee (if using), and vanilla extract.

Pour the wet ingredients into the dry ingredients and whisk just until the batter comes together. A few lumps are okay.

Fill cupcake liners about ⅔ full and bake for about 12-15 minutes, or until a toothpick inserted into the center comes out clean. Cool completely before frosting.

While the cupcakes are cooling, prepare the chocolate buttercream frosting. Beat the softened butter in a large bowl with an electric mixer until creamy. Add the cocoa powder and beat until combined.

Gradually add the powdered sugar, alternating with the heavy cream, beating until smooth and creamy. Stir in the vanilla extract.

Once the cupcakes are completely cool, frost them as desired.