1-Step 1: Prepare the Raspberry Sauce: Combine 12 ounces of fresh or frozen raspberries, 3 tablespoons of granulated sugar, and 2 tablespoons of fresh squeezed lemon juice in a saucepan. Bring the mixture to a boil while mashing the berries until they soften, then strain it through a fine-mesh sieve to remove the seeds. Return the liquid to the saucepan and cook over medium heat until it’s reduced by half, yielding about 6-7 tablespoons of concentrated coulis. Let it cool completely to room temperature before using.

2-Step 2: Make the Meringue Base: Place 5 large egg whites and 1¼ cups of granulated sugar in a mixing bowl set over simmering water. Stir constantly until the mixture reaches 170°F and the sugar dissolves fully, which ensures safety and smoothness.

3-Step 3: Whip the Meringue: Transfer the bowl to a stand mixer with a whisk attachment and whip at medium-high speed until the meringue cools to about 80-85°F and forms soft peaks. This step builds the airy structure that makes the buttercream so light.

4-Step 4: Incorporate the Butter: Add the 30 tablespoons of unsalted butter, at room temperature (65-68°F), one tablespoon at a time while mixing on medium speed. The mixture might look curdled at first, but keep going until it turns smooth and creamy, like thick whipped cream.

5-Step 5: Add Flavorings: Beat in 1 teaspoon of pure vanilla extract, then mix in 2 tablespoons of the cooled raspberry sauce. Add more sauce one tablespoon at a time until you reach your desired berry intensity. Once done, use the frosting right away for the best texture.