Preheat oven to 350º.
Coat bottom of a 9-inch square baking pan with cooking spray.
Combine coffee and hot water, stirring until coffee dissolves.
Combine butter and chocolate chips in a small microwave-safe bowl. Microwave at high 1 minute or until butter melts; stir until chocolate is smooth.
Lightly spoon flour into dry measuring cups; level with a knife. Combine flour, sugar, cocoa, baking powder, and salt in a large bowl, stirring with a whisk. Combine coffee mixture, butter mixture, vanilla, and eggs in a medium bowl, stirring with a whisk. Add coffee mixture to flour mixture; stir just until combined. Spread evenly into prepared pan. Sprinkle evenly with toffee chips. Bake at 350º for 22 minutes. Cool on a wire rack.
Note: Store leftover brownies in an airtight container for up to a week or wrap tightly in aluminum foil and freeze for up to four months.