Lightly coat 9 by 13-inch baking pan with butter-flavored cooking spray. In a large saucepan over medium heat, combine butter, sugar, evaporated milk, and espresso powder. Stirring constantly, bring to a rolling boil for 10 minutes.
Remove from heat and stir in chocolate chips and marshmallows until blended. Pour into prepared pan. Sprinkle toffee chips evenly over fudge and pat lightly. Cool until set, about 3 to 4 hours. Cut into bite-sized squares.
Recipe courtesy of Sandra Lee