Preheat your oven to 350 degrees Fahrenheit and line a 9 x 13 dish with parchment paper.
In a large bowl, mix 2 cups of flour, 3/4 cup of cold butter, 1/3 cup white sugar, and 1/3 cup brown sugar. Use a pastry blender or your fingers to mix it until it is crumbly.
Dump the flour mix into your baking dish and press mixture down evenly.
Bake for 15 minutes. Set aside to cool.
Meanwhile, make the filling by mixing 1/2 cup of butter, 4 eggs, 2 tsp baking powder, 2 cups of brown sugar, 2 tbsp of flour, and 1 tbsp of vanilla.
Set aside filling and spread out evenly over your crust 1/4 cup of chocolate chips and 1/4 cup of toffee bits.
Pour the filling mixture over the crust and spread evenly with a spatula.
Bake for 30 minutes, until it's golden brown, the edges are firm but the middle is slightly jiggly, but not too much. You want the filling to be set.
Let it cool for 5 minutes.
After the 5 minutes sprinkle the remaining Skor toffee bits and chocolate chips. Press them down gently into the top of the butter tart squares. You want to work fast doing this because the chocolate chips will start to melt and make a mess.
Let the squares completely cool before serving.