Preheat oven to 350 degrees F. Butter the bottom and sides of a 9-by-13-inch baking pan. Put a long piece of parchment paper in the bottom of the pan, letting the parchment extend up the two short sides of the pan and overhang slightly on both ends.

In a medium bowl, whisk together flour, baking powder, salt and cinnamon; set aside.

In the bowl of a stand mixer fitted with a paddle attachment, cream the butter and brown sugar at medium speed until light and fluffy, about 2 minutes. Scrape down the sides of the bowl with a rubber spatula as needed. Add the eggs, one at a time, beating until well combined. Add the vanilla and beat until combined. Add the dry ingredients and beat at low speed until just combined, about 30 seconds, scraping down the bowl as needed. Fold in chopped apples and toffee bits. (Batter will be thick)

Spread the batter into the prepared pan. Bake 25- 30 minutes, or until center is set and toothpick inserted into the center come out clean. Place on wire rack to cool completely before slicing or frosting.

To make the frosting, melt butter in a small saucepan over low heat. Stir in brown sugar and milk. Bring mixture to a boil then remove from heat and let cool to lukewarm. Sift in the confectioner’s sugar, mixing until smooth. Spread evenly over blondies. Let frosting set before cutting into squares, about 30 minutes.