Preheat oven to 350°F (175°C). Line 2 muffin tins with baking papers.

Whisk together boiling water and cocoa powder until smooth. Let cool completely.

Whisk Bailey's Irish Cream into the cooled cocoa mixture.

In a stand mixer, beat sugar, butter, and vanilla extract until light and fluffy.

Add eggs one at a time, beating well after each addition.

In a separate bowl, whisk together flour, baking soda, baking powder, and salt.

Gradually add the dry ingredients to the wet ingredients, alternating with the cocoa mixture, beginning and ending with the flour mixture. Mix until just combined.

Fill each baking cup 2/3 full with batter.

Bake for 12-15 minutes, or until a toothpick inserted into the center comes out clean.

Let the cupcakes cool in the pans for 2 minutes on a wire rack.

Carefully remove the cupcakes from the pans and cool completely before frosting.

For the buttercream, beat butter until light and fluffy.

Gradually add powdered sugar, 1 cup at a time, until smooth.

Add Bailey's Irish Cream and cinnamon. Beat on medium speed until light and fluffy.

Fit a pastry bag with a large round tip.

Pipe a fluffy cloud of buttercream onto each cupcake.

Sprinkle with grated chocolate or colored jimmies.

Store leftover cupcakes in an airtight container at room temperature up to 2 days.