Preheat your oven to 350°F (175°C). Grease an 8x8 inch baking pan and line it with parchment paper, leaving an overhang on two sides for easy removal.

In a small saucepan, combine the raspberries and 1 tablespoon of sugar. Cook over medium heat, mashing the berries with a spoon for 5 to 7 minutes until thickened into a jam-like consistency. Remove from heat and cool. Strain through a fine mesh sieve if desired for smoother texture.

In a medium bowl, beat the softened cream cheese and 1/4 cup of sugar with an electric mixer until smooth and creamy. Add the egg yolk and vanilla extract, beating until just combined. Fold in about two-thirds of the cooled raspberry sauce, leaving ribbons for swirling.

In a large bowl, whisk together the melted butter and 1 cup of granulated sugar. Add eggs one at a time, whisking after each. Stir in the vanilla extract.

In a separate bowl, whisk together the flour, cocoa powder, baking powder, and salt. Gradually add to the wet ingredients, mixing until just combined. Fold in chocolate chips if using.

Pour the brownie batter into the prepared pan and spread evenly. Dollop the raspberry cream cheese mixture on top, then add spoonfuls of the remaining raspberry sauce.

Use a knife or skewer to gently swirl the layers, creating a marbled effect without overmixing.

Bake for 30 to 35 minutes, or until a toothpick inserted into the brownie portion comes out with moist crumbs. Cool completely in the pan on a wire rack before cutting.