Position a rack in the center of your oven and preheat to 350. Line an 8x8 pan with parchment paper, leaving an overhang on opposite sides.

Melt the butter and chocolate in the microwave, on 50% power in 30 second intervals. Stir smooth. Mix in the sugar and salt.

Whisk in your eggs, 1 at a time, and then whisk in the vanilla extract and vanilla bean paste/powder. Gently fold in the flour. Scrape the batter into the prepared pan—it will be thick.

Dollop the lime curd on top of the brownie batter by tablespoonfuls. Using a butter knife, swirl the curd into the batter. Bake for 25 to 28 minutes, or until a toothpick inserted in the center comes out clean.

Transfer pan to a wire rack and allow to cool completely. Using the parchment overhang, lift out the entire block and cut into squares. Try not to eat all at once.