Preheat oven to 325°F (162°C) and line an 8-inch square baking pan with parchment paper or aluminum foil.

Melt the butter in a medium saucepan over medium-low heat until completely melted, then turn off the heat.

Stir in the sugar, cocoa powder, vanilla, and salt until well blended.

Let the mixture cool slightly until warm, not hot.

Add the eggs one at a time, stirring vigorously after each addition.

Beat in the flour until thick and the batter pulls away from the sides of the bowl.

Stir in optional nuts or chocolate chips if using.

Scrape the batter into the prepared pan and spread it evenly. Bake for 20 to 30 minutes until the edges look set and the center is slightly underbaked.

Allow the brownies to cool completely in the pan before slicing.