In a small saucepan, add the raspberries, sugar and water. Cook over medium-low heat for 5 minutes, stirring occasionally.
1 cup raspberries, ¼ cup sugar, 1 tablespoon water
Transfer raspberry mixture to a blender leaving the top ajar to allow steam to escape. Puree raspberry mixture until smooth.
Pour the raspberry mixture back into the saucepan through a fine mesh sieve, using a whisk to stir the sauce through the sieve. Discard the remaining solids in the fine mesh sieve.
Return the pan to medium-low heat and continue to cook for 10 minutes or until thickened. Remove from heat and let cool slightly.
Preheat oven to 350°F. Line a square baking pan with parchment paper or coat with cooking spray.
Heat butter in a small saucepan over medium heat until melted. Remove from heat and add the chopped dark chocolate. Stir until fully melted and smooth. Set aside to cool slightly.
8 tablespoons unsalted butter, 3.5 ounces 70% cocoa dark chocolate bar, coarsley chopped
In a medium bowl, combine the brown sugar, egg, egg yolk and vanilla. Stir with a whisk until well combined.
¾ cup packed brown sugar, 1 egg, 1 egg yolk, 2 teaspoons vanilla
Add the chocolate mixture to the brown sugar mixture and stir with a whisk until fully combined.
Add the flour, baking powder, salt and chopped chocolate to the chocolate mixture. Using a rubber spatula, fold in the ingredients just until combined.
1 cup flour, ½ teaspoon baking powder, ½ teaspoon salt, 1 cup chocolate, coarsley chopped
Transfer mixture to prepared baking pan. Spread evenly.
Drop the raspberry sauce in tablespoonfuls all over the top of the batter. Using a knife, drag it through the batter and raspberry sauce to create swirls in the top, making sure to go all the way to the edges.
Bake in 350°F oven for 25-27 minutes.
Remove from the oven and let cool completely before cutting into squares.