Preheat the oven to 350°F (175°C). Grease a 9x13 inch baking pan or line it with parchment paper.
In a medium saucepan over low heat, melt the butter and chopped chocolate together, stirring until smooth. Remove from heat and let it cool slightly.
In a large mixing bowl, combine the granulated sugar, brown sugar, and eggs. Whisk until well combined. Stir in the melted chocolate mixture and vanilla extract.
Add the flour and salt to the chocolate mixture, stirring until just combined. Be careful not to overmix.
Gently fold in the sliced strawberries and chocolate chips, if using.
Pour the brownie batter into the prepared baking pan, spreading it evenly.
Bake for 25-30 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.
Allow the brownies to cool in the pan for at least 15 minutes before slicing into squares. For best flavor, chill in the refrigerator for an hour before serving.