Preheat oven to 350 degrees Fahrenheit. Line a 8x8-inch pan with foil; set aside.
In a double-boiler over gently simmering water, melt 1 cup chocolate chips and the butter. Stir until smooth and all of the chips have completely melted. Remove from, heat and cool for 5-10 minutes.
Stir in white sugar and brown sugar. Add eggs, one at a time, stirring well to combine. Stir in vanilla extract.
In a small bowl, sift the flour and salt. Stir into chocolate mixture until no white streaks remain.
Fold in the remaining 1 cup semisweet chocolate chips and 1/4 cup toffee bits. Pour batter into prepared pan. Scatter remaining 1/4 cup toffee bits over the top. (You can stir in 1/2 cup semisweet chocolate chips into the batter and scatter the remaining 1/2 cup semisweet chocolate chips on top of the batter, along with the 1/4 cup toffee bits, if you'd like, instead of stirring the entire 1 cup of semisweet chocolate chips into the batter.).
Bake at 350 degrees Fahrenheit for 25-28 minutes, or until top is dry and lightly browned, rotating pan halfway during baking time.
Remove pan from oven to a wire rack to cool completely. Lift foil out of pan and set onto a cutting board. Remove foil from large bar. Cut into 32 brownies.