Preheat your oven to 350°F (175°C). Line a 9x13 inch baking pan with parchment paper or foil, leaving an overhang on the sides for easy lifting. You can also lightly spray the bottom with cooking spray if you prefer.

In a medium bowl, whisk together the all-purpose flour, baking soda, and kosher salt. Set this dry mixture aside for later.

In a large mixing bowl, combine the brown sugar, white sugar, and melted, slightly cooled butter. Mix thoroughly until the sugars are fully incorporated into the butter and the mixture is smooth.

Add the large eggs to the sugar-butter mixture, one at a time, stirring well after each addition. Stir in the vanilla extract until fully combined.

Gradually add the dry flour mixture to the wet ingredients, mixing on low speed or by hand until just combined. Be careful not to overmix the dough, as this can lead to tough bars.

Fold in the chocolate chips. If you want to make them extra pretty, reserve a small handful of chips to sprinkle on top before baking.

Press the dough evenly into the prepared 9x13 inch baking pan. If you're using optional toffee bits, sprinkle them evenly over the top of the pressed dough.

Bake for 25-35 minutes. Start checking at 25 minutes. The bars are done when the edges are golden brown and the center appears mostly set but still slightly soft and gooey. Remember, they will continue to set as they cool.

Remove the pan from the oven and let the bars cool completely in the pan on a wire rack. This is crucial! If you cut them while warm, they will be very soft and fall apart. Once fully cooled, use the parchment or foil overhang to lift the entire slab of bars out of the pan and cut into squares.