1. In a small saucepan, combine 1 cup of raspberries (fresh or thawed frozen). Cook over medium heat, stirring occasionally, until the raspberries break down and release their juices. Simmer until slightly thickened (about 5–7 minutes), then strain through a fine mesh sieve to remove seeds. Let cool completely.

2. In a large mixing bowl, beat 1 cup (2 sticks) of unsalted butter at medium-high speed for 2–3 minutes until pale and fluffy.

3. Gradually add 3 1/2 cups powdered sugar, 1/2 cup at a time, beating on low until incorporated. Increase speed to medium and beat until light and fluffy.

4. Add 1/4 cup of the cooled raspberry puree (add more for deeper color or flavor, up to 1/3 cup), 1 teaspoon vanilla extract, and a pinch of salt. Beat until the frosting is smooth and silky. Scrape down the sides as needed.

5. If the frosting is too soft, add a bit more powdered sugar (1 tablespoon at a time). If it’s too stiff, add a teaspoon of milk or remaining raspberry puree.