Preheat the oven to 350°F (175°C) and line an 8x8-inch pan with parchment paper.
Melt butter and mix with brown sugar until smooth.
Whisk in eggs, vanilla, and espresso powder until fully combined.
Sift in flour, baking powder, and salt and fold gently until just mixed.
In a saucepan, melt sugar until golden and stir in butter, cream, and sea salt to create caramel.
Pour blondie batter into the pan, then swirl in caramel using a knife.
Bake for 25 minutes, until edges are set but the center is slightly gooey.
Cool for at least 20 minutes before cutting (if you have the patience).
Slice into squares and serve warm or at room temperature.
Enjoy immediately or store in an airtight container for up to four days