Cream together butter and brown sugar until smooth and fluffy. Add in egg yolk and vanilla, mix well. Then stir in the flour and 1 cup of the toffee bits.

On a parchment lined rimmed baking sheet, spread out mixture and flatten evenly with hands to make a crust. Bake at 350°F for 18-20 minutes, until lightly browned.

Immediately remove from oven and sprinkle the chocolate chips over the hot crust. Let sit for 5 mintues, then start to spread out the melted chocolate evenly over crust. Sprinkle the remaining 1/4 cup toffee bits over the chocolate, then chill until chocolate is set (1 hour).