Stir the espresso instant coffee and vanilla together in a small container until the instant coffee dissolves into the vanilla.
Beat butter, sugar, and baking powder together in a large mixing bowl with an electric mixer until fluffy.
Stir in the egg and coffee mixture into the mix.
Slowly beat in the flour until incorporated.
Divide the dough in half and roll each half on a lightly floured surface into a 9-inch log.
Wrap each log in plastic wrap and refrigerate for 4 hours until firm.
Cut in 1/2-inch slices and place on a greased baking sheet (or line with parchment paper) about 2 inches apart.
Top each cookie with a 1/2 teaspoon toffee bits and press lightly.
Bake at 350° degrees for 10-12 minutes. Edges will be slightly browned.
Cool for 3 minutes before moving to a rack to cool completely.