Preheat the oven to 350°F (175°C).
Prepare a 9x13 inch baking pan by greasing it or lining it with parchment paper.
Melt the butter in a medium saucepan over low heat, then remove from heat and stir in the sugar.
Add the eggs and vanilla to the butter-sugar mixture, mixing until well combined.
Sift together the flour, cocoa powder, and salt before folding it into the wet ingredients.
Gently fold in the diced strawberries and chocolate chips, if using.
Pour the batter into the prepared baking pan and spread it evenly.
Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted comes out with moist crumbs.
Allow the brownies to cool in the pan before slicing and serving.