Preheat the oven to 350°F (175°C). Line a standard muffin pan with paper liners or lightly coat with nonstick cooking spray. Dissolve the espresso powder in the boiling water and set aside to cool.

In a large mixing bowl, cream the shortening and granulated sugar together until light and fluffy. Add the eggs one at a time, beating well after each addition.

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

Gradually add the dry ingredients to the creamed mixture, alternating with the cooled espresso mixture, mixing until just combined. Gently fold in the milk chocolate toffee bits.

Fill the prepared muffin cups approximately three-fourths full. Bake for 20–22 minutes, or until a toothpick inserted into the center comes out clean. Transfer the pan to a wire rack and allow the cupcakes to cool for 10 minutes before removing them from the pan. Let the cupcakes cool completely before frosting.

In a small bowl, mix the espresso powder with the vanilla extract until fully dissolved. In the bowl of a stand mixer fitted with the whisk attachment, whip the butter on medium-high speed for 5 minutes, stopping once to scrape down the sides of the bowl.

Reduce the mixer speed to low and gradually add the powdered sugar, allowing it to incorporate before adding more. Once all the sugar has been added, scrape down the bowl and increase the speed to medium-high. Whip until light and fluffy, approximately 1–2 minutes. Add the espresso-vanilla mixture and continue mixing until fully incorporated.

Frost the cooled cupcakes with the espresso buttercream. Garnish with additional toffee bits or chocolate chips, if desired.