Preheat your oven to 350°F (175°C). Grease a 9x13 inch baking pan or line it with parchment paper for easy removal.
In a medium saucepan, melt the butter over low heat. Once melted, add in the granulated sugar and stir until combined and slightly cooled.
Remove the saucepan from the heat and mix in the eggs, one at a time, stirring well after each addition. Add in the vanilla extract.
In a separate bowl, whisk together the flour, cocoa powder, and salt. Gradually fold the dry ingredients into the wet mixture until just combined. Stir in the chocolate chips if using.
Pour the brownie batter into the prepared baking pan, spreading it evenly.
In a mixing bowl, beat the softened cream cheese with the sugar until smooth. Add the egg and vanilla extract, mixing until fully combined and creamy.
Gently fold in the raspberries into the cream cheese mixture. It’s okay if some of them break apart, but try to leave some whole for texture.
Drop dollops of the raspberry cheesecake mixture over the brownie batter. Use a knife or toothpick to swirl the two mixtures together, creating a marbled effect.
Bake in the preheated oven for 30-35 minutes, or until a toothpick inserted into the center comes out mostly clean with a few moist crumbs.
Allow the brownies to cool in the pan for about 15 minutes, then carefully lift them out using the parchment paper, if used. Let them cool completely on a wire rack before cutting into squares.
Notes
Allow brownies to cool completely before cutting for best texture.