Preheat oven to 325°F and butter an 8-inch square baking pan.

In a small bowl, whisk together flour, baking soda, and salt.

In a saucepan over medium heat, stir together sugar, butter, and milk until it boils. Remove from heat and stir in 1½ cups chocolate morsels until smooth.

Add eggs and vanilla to the chocolate mixture and stir until blended.

Gradually add flour mixture to the chocolate mixture, stirring until just combined.

Spread batter evenly into the pan and sprinkle remaining 1 cup of chocolate morsels on top.

Bake for 25–30 minutes, rotating the pan halfway through.

Cool in the pan on a wire rack. Cut into 6 squares and serve with vanilla ice cream and chocolate sauce if desired.