Preheat oven to 350°F (175°C). Line an 8-inch square baking pan with parchment paper, leaving overhang on two sides. Lightly spray with cooking spray.

Make raspberry sauce: Combine raspberries, 1/2 cup sugar, and water in a saucepan over medium heat. Stir until sugar dissolves, then mash berries with a spoon or immersion blender. Bring to a boil and cook 2 to 3 minutes until thick and jammy. Strain through fine-mesh sieve to remove seeds. Set aside to cool.

In a larger saucepan, melt butter and chocolate chips over low heat, stirring frequently until smooth. Remove from heat and let cool for 10 minutes (can place in refrigerator to speed cooling).

In a separate bowl, whisk together eggs, 1 cup sugar, and vanilla extract until well combined and slightly frothy.

Slowly pour egg mixture into cooled chocolate mixture while stirring constantly to temper the eggs and prevent scrambling.

Add flour, salt, baking powder, and baking soda to chocolate mixture. Fold gently just until no flour streaks remain - do not overmix.

Pour batter into prepared pan and spread evenly. Spoon small dollops of raspberry sauce over the surface, then drag a knife through in swirling motions to create a marbled pattern.

Bake for 30 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs (not wet batter). Do not overbake.

Let brownies cool completely in the pan for at least 2 hours before cutting. Lift out using parchment overhang, then cut into 16 squares with a sharp knife, wiping clean between cuts.