In a small saucepan, combine fresh raspberries, sugar, and a splash of water. Cook over medium heat for 5–7 minutes, stirring occasionally until the mixture thickens and becomes syrupy. Strain the sauce for a smooth consistency, then set aside to cool.

Preheat your oven to 350°F (175°C). Line an 8x8-inch baking dish with parchment paper, allowing some overhang for easy removal.

Melt the semi-sweet chocolate chips and butter together over low heat in a medium saucepan, stirring gently until smooth. Let cool slightly.

In a large bowl, whisk together large eggs, granulated sugar, and vanilla extract until frothy. Gradually pour in the cooled chocolate and butter mixture while whisking to combine.

Sift together all-purpose flour, baking powder, baking soda, and salt in a separate bowl. Gently fold these dry ingredients into the wet mixture using a spatula.

Pour half of the brownie batter into the prepared baking pan. Drizzle half of the cooled raspberry sauce over the batter, then layer with remaining brownie batter. Top with remaining raspberry sauce and swirl.

Bake for 30 minutes. Check for doneness by inserting a toothpick into the center; it should come out with moist crumbs.

Let the brownies cool in the pan for at least 10 minutes. Lift them out using the parchment overhang and transfer to a wire rack to cool completely before slicing.