For the cupcakes:
Prepare bacon via your preferred method until crispy. I baked my bacon in the oven at 375F for about 14 minutes. Place bacon on paper towels to drain the fat and pat dry. Finely chop the bacon, but reserve 1-2 strips to cut into 1-inch or so squares to top cupcakes.
Preheat the oven to 325 degrees. Line cupcake pans with 24 cupcake liners.
Sift flour, cocoa powder, salt, baking powder, baking soda, and sugar together into a medium bowl.
Combine the egg, milk, oil, vanilla, and dissolved espresso powder in a medium bowl and whisk by hand until well mixed. Pour wet ingredients into the dry ingredients and whisk to combine. Fold in finely chopped bacon and chocolate chips.
Divide the batter evenly among the muffin cups, filling them about ¾ full.
Bake for about 15-20 minutes, until the cupcakes are puffed and feel springy. Let cool completely in the pan on a wire rack.
For the frosting:
Finely chop or crush toffee and set aside. In large bowl, combine butter, peanut butter, sugar, salt, vanilla, and 2 tablespoons milk. Mix well, adding more milk as needed to make a fluffy spreadable frosting. Frost cupcakes and sprinkle or roll in chopped/crushed toffee. Top with a square of bacon if desired.