Pre-heat oven to 350° and grease a 10×15” Jelly roll pan.
In large bowl mix:
3 ½ cups flour
1 cup brown sugar
1 egg, plus 1 egg yolk
3 cups of semi sweet chocolate chips
1 ½ cup coarsely chopped nuts
1 ½ cans sweetened condensed milk
15 oz toffee chips
Stir flour and brown sugar together then cut in butter until coarse and crumbly.
Add eggs and mix well.
Stir in 2 cups chocolate chips and all of the nuts.
Reserve 3 cups of the crumb mixture.
Press remaining crumb mixture into the jelly roll pan and bake 10 minutes or until lightly browned.
Remove from oven and pour sweetened condensed milk over hot crust, leaving a slight rim around the edges uncovered.
Top with 10 oz toffee chips.
Sprinkle reserved crumb mixture and chocolate chips over the top.
Bake 20-25 minutes then sprinkle the remaining 5 oz of toffee chips over the top.