1. Preheat the oven to 200°F (95°C). Line a baking sheet with parchment paper.

2. In a clean, dry bowl of a stand mixer fitted with the whisk attachment, beat the egg whites on medium-high speed until they start to become frothy.

3. Gradually add the granulated sugar, 1-2 tablespoons at a time, beating well after each addition, until the meringue is stiff and glossy.

4. In a small saucepan, combine the heavy cream, brown sugar, and salt. Cook over medium heat, stirring frequently, until the mixture comes to a boil and the sugar has dissolved, about 5 minutes.

5. Remove from heat and stir in the vanilla extract. Allow the caramel to cool slightly.

6. Using a piping bag fitted with a large open star tip, pipe the meringue into 6 equal-sized mounds on the prepared baking sheet.

7. Bake for 1 hour, then turn off the oven and leave the meringues inside for an additional 30 minutes.

8. Remove the meringues from the oven and let cool completely.

9. In a small bowl, beat the butter until smooth and creamy. Slowly drizzle in the salted caramel, beating until well combined.

10. Pipe or spoon the salted caramel buttercream onto the cooled meringues.