Prepare Raspberry Sauce: In a saucepan, combine fresh raspberries, sugar, and a splash of water over medium heat for about 5 minutes until saucy. Strain to remove seeds and cool.

Preheat Oven: Preheat oven to 350°F (175°C). Line an 8-inch baking pan with parchment paper.

Melt Chocolate and Butter: In a saucepan, melt chocolate chips and butter over low heat, stirring until smooth. Let cool slightly.

Mix Wet Ingredients: In a bowl, whisk eggs, sugar, and vanilla until smooth. Stir in melted chocolate mixture until combined.

Combine Dry Ingredients: In another bowl, whisk flour, salt, baking powder, and baking soda. Gradually add to wet ingredients, mixing gently.

Layer and Swirl: Spread half of the batter in the pan, drizzle half of the raspberry sauce, then add remaining batter and swirl the top with remaining sauce.

Bake: Bake for 30 minutes until edges are set; center should be slightly soft. Test with a toothpick.

Cool and Slice: Cool brownies in the pan for 1 hour, then transfer to a wire rack to cool completely before slicing.