Preheat your oven to 350°F (175°C) and line an 8×8-inch baking pan with parchment paper.

In a small saucepan, combine raspberries, sugar, and lemon juice. Cook over medium heat for about 5–7 minutes, mashing gently until a thick purée forms. Remove from heat and set aside to cool.

In a separate saucepan, melt the butter and chopped chocolate over low heat, stirring until smooth. Once fully melted, remove from heat.

Whisk the granulated sugar into the chocolate mixture. Next, add the eggs one at a time, whisking well after each addition. Stir in the vanilla extract.

In another bowl, sift together the flour, cocoa powder, and salt. Fold the dry ingredients into the wet mixture using a spatula, ensuring everything is fully combined.

Pour the brownie batter into the prepared baking pan and spread it evenly.

Drop spoonfuls of raspberry purée on top and gently swirl it through the batter using a knife to create a marbled effect.

Bake in the preheated oven for 25–30 minutes, or until the edges are set and the center is still slightly fudgy.

Allow the brownies to cool completely in the pan before slicing for the best texture and clean edges.