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1
Line an 8x8-inch baking pan with parchment paper.
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2
Make browned butter: Add the butter to a small saucepan and set over medium to medium-high heat. Cook, watching like a hawk and stirring occasionally, until it foams, smells super nutty, and the solids at the bottom begin to turn the color of toasted bread. Remove from heat (it'll brown a bit more as it sits) and transfer to a bowl, giving it a stir-let it hang out while you melt the chocolate.
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3
Melt the chocolate: You can do this in a double boiler, or in a big bowl in short bursts in the microwave. Stir frequently until just melted (keep in mind that as you stir, the chocolate continues to melt).
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4
Add the browned butter, sweetened condensed milk, espresso powder, and 1/2 teaspoon salt to the melted chocolate, and stir until combined. The mixture will become thick, like wet soil, as you stir. Taste and add another pinch of salt if it's feeling too sweet-but keep in mind, you'll sprinkle a bit more on top to finish the fudge.
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5
Transfer the thick mixture into the prepared pan and use a damp spatula to smooth over the top as needed (your hand works, too!). Sprinkle the top with a pinch of salt.
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6
Cover and refrigerate for at least 90 minutes, until set and easily sliceable into 1x1-inch squares. If you're having trouble cutting through the chilled fudge, try using a warm knife: run it under hot water, then dry it off before slicing. Store covered in the fridge for up to a week, or wrap tightly and freeze for a month. This is best served at room temperature.
