Step 1: Preheat the oven to 300°F (150°C) and line a baking sheet with parchment paper

Step 2: In a medium bowl, sift together the almond flour and confectioners' sugar

Step 3: In a large bowl, whip the egg whites until stiff peaks form, then gradually add the granulated sugar

Step 4: Add the sifted almond flour mixture to the egg mixture and fold until well combined

Step 5: Transfer the mixture to a piping bag and pipe small, round circles onto the prepared baking sheet

Step 6: Tap the baking sheet gently to remove any air bubbles and allow the macarons to sit at room temperature for 30 minutes

Step 7: Bake the macarons for 15 minutes, then allow them to cool completely on the baking sheet

Step 8: To make the salted caramel filling, combine the heavy cream, unsalted butter, and fleur de sel in a small saucepan and cook over medium heat, stirring constantly, until the caramel turns a deep amber color

Step 9: Allow the caramel to cool and thicken slightly, then pair up the macarons by size and shape

Step 10: Sandwich a small dollop of the salted caramel filling between two macarons and serve immediately