Line a 9x13” pan with foil and spray with cooking spray. Preheat oven to 350°F.
Place butter, flour, salt and powdered sugar in the bowl of a stand mixer fitted with the paddle attachment (or use a hand mixer). Mix until smooth. Stir in 1/4 cup chopped almonds. The mixture will be wet to the touch.
Place shortbread in the prepared pan. Spray your hands with cooking spray and press to a thin layer in the pan. Bake shortbread layer for 15 minutes.
While the crust is baking, stir together sweetened condensed milk, egg, and vanilla. Stir in toffee bits, chocolate chips, and remaining 1/2 cup chopped almonds. After 15 minutes of baking, pour the milk mixture carefully over the hot crust. Continue baking for about 18 minutes until the sides start to look golden brown.
Cool completely before cutting into bars. Store in an airtight container for up to 3 days or freeze for up to one month.