Preheat your oven to 350°F (175°C) and prepare an 8x8-inch baking pan.

In a large mixing bowl, whisk together melted unsalted butter and brown sugar until smooth, then add eggs, vanilla extract, and instant espresso powder.

In a separate bowl, sift together flour, baking powder, and salt, then fold into the wet ingredients until just combined.

Melt granulated sugar in a saucepan over medium heat until golden, then add unsalted butter, stir until smooth, then mix in heavy cream and sea salt.

Pour the blondie batter into the prepared pan, drizzle with caramel sauce, and swirl with a knife.

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

Cool in the pan for 10 minutes, then transfer to a wire rack to cool completely before slicing.