Start by preheating your oven to 350°F (175°C). In a bowl, combine the butter, flour, and brown sugar to create a crumbly mixture. Press this evenly into a 9x13-inch baking pan to form the crust. Bake the crust for about 15 minutes, or until it turns a golden brown.

In a saucepan, heat the sweetened condensed milk over medium heat, stirring frequently to avoid burning. Once heated, remove it from the stove and stir in the vanilla extract. Pour this creamy mixture over the baked crust and sprinkle the chopped pecans and toffee bits evenly on top.

Return the pan to the oven and bake for an additional 20-25 minutes until the top is golden and bubbly. This ensures the toffee melts perfectly and binds with the pecans and crust.

Let the bars cool in the pan for about 30 minutes. Once cooled, transfer the pan to the fridge to firm up further. After about an hour, cut the bars into squares and get ready to indulge!