Preheat the oven to 350°F (175°C). Grease the baking pan.

In a mixing bowl, combine flour, brown sugar, melted butter, and salt. Mix until crumbly.

Press the mixture evenly into the bottom of the prepared baking pan.

In a separate bowl, mix chocolate chips and sweetened condensed milk until well combined.

Pour the filling over the base and spread evenly. Sprinkle chopped nuts on top if desired.

Bake in the preheated oven for 25 minutes or until the edges are golden brown.

Remove from the oven and let cool in the pan for at least 10 minutes.

Cut into bars and serve warm or at room temperature.