Preheat your oven to 350°F (175°C) and prepare an 8x8-inch baking dish by greasing it with butter or lining it with parchment paper.

In a mixing bowl, whisk together the flour, granulated sugar, and salt until well combined.

Pour in the melted butter, egg, and vanilla extract into the dry mix, stirring until the batter is smooth.

Spread the batter into the prepared baking dish evenly.

In another bowl, mash the raspberries with lemon juice and lemon zest, mixing well.

Drop spoonfuls of the raspberry mixture over the batter and gently swirl with a knife.

Bake for 25-30 minutes until edges are golden and a toothpick comes out clean.

Let cool in the pan for 10 minutes, then transfer to a wire rack to cool completely before dusting with powdered sugar and slicing.