Preheat your oven to 350°F. Grease (or line with parchment or non-stick foil) a 13"x9" baking pan
Combine the flour, sugar and salt in a large bowl. Add the butter, using a pastry cutter, large fork or a pair of butter knives, cut the butter into the dry ingredients until it resembles coarse crumbs.
2 1/3 cup flour, 2/3 cup brown sugar, 1/2 tsp salt, 3/4 cup butter
Add the egg and vanilla and mix until it starts to come together in a crumbly dough. Stir in 1 1/2 cups of the chocolate chips and (if you are using them) the coarsely chopped nuts. Set aside 1 1/2 cups (300g) of the mixture (this will be the top of the bars).
1 egg, 1/2 tsp vanilla, 1 ½ cups chocolate chips, 1 cup nuts
Press the remaining mix onto the bottom of the prepared pan and bake in the preheated oven for 10 minutes.
Remove from the oven and immediately pour the sweetened condensed milk over the hot crust. Top the condensed milk with 8 1/2 oz of toffee bits.
14 oz sweetened condensed milk, 8 ½ oz English Toffee bits.
Sprinkle the reserved crumb mixture and the remaining chocolate chips over the top of the toffee bits.
½ cups chocolate chips
Bake in the preheated oven for 25-30 minutes or until it is golden brown.
Remove from the oven and sprinkle the remaining 1 1/2 oz of toffee bits and the flaky sea salt evenly over the surface.
1 ½ oz English Toffee bits., 1/2 - 1 tsp flaky sea salt
Cool completely on a wire rack before cutting into bars (40 small, 32 medium or 24 large). Store in an air tight container at room temperature.