1-First, let’s make the balsamic caramel as the base. Combine 1/2 cup light brown sugar and 1/4 cup balsamic vinegar in a saucepan and bring to a boil. Simmer for about 3 minutes until it thickens, then carefully add 1/2 cup heavy cream. Bring it back to a boil and simmer for 2 to 4 minutes until thick, then stir in 1 tablespoon butter and 1/4 teaspoon salt until melted. Let the caramel cool completely before moving on this is key for the next steps!

2-Now, for the buttercream itself, remove the butter from the fridge about 30 minutes ahead to soften it. In a heatproof bowl, whisk 4 large egg whites and 1 cup granulated sugar over a double boiler until they reach 140°F (60°C). Transfer this mixture to a mixer and whip at medium speed for 2 minutes until it’s white and thick, then crank it up to high speed and whip for 5 to 10 minutes until stiff peaks form. Add the softened 20 tablespoons butter one tablespoon at a time, mixing continuously for about 5 to 10 minutes until it’s creamy and fluffy. Stir in 1 teaspoon vanilla extract, then gently fold in 1/2 cup of the cooled balsamic caramel.

3-Key Steps for Success

1. Gather all ingredients and ensure egg whites are at room temperature for optimal whipping.

2. In a heatproof bowl, combine egg whites and granulated sugar; heat over a double boiler until the mixture reaches 160°F, dissolving the sugar fully.

3. Transfer to a stand mixer and whip on high speed until stiff, glossy peaks form and the mixture cools to room temperature.

4. Gradually add softened unsalted butter, one tablespoon at a time, mixing well after each addition until smooth and creamy.

5. Slowly incorporate balsamic vinegar and caramel sauce, folding gently to maintain airiness.

6. Use immediately to frost cakes or cupcakes, or refrigerate the buttercream; allow to come to room temperature and re-whip before serving.