01 - Place lavender buds in a small bowl. Pour boiling water over them and steep for 10 minutes. Strain to remove the buds and let the infused liquid cool.
02 - In a large mixing bowl, beat softened butter on medium-high speed until creamy and pale, about 3 minutes, using an electric mixer.
03 - Gradually add powdered sugar, one cup at a time, beating on low speed after each addition until fully incorporated.
04 - Pour in the cooled lavender infusion, vanilla extract, and heavy cream or milk. Continue to beat on medium-high speed until the mixture is light and fluffy, about 2 to 3 minutes.
05 - If desired, add a small drop of purple food coloring to achieve a soft lavender hue. Mix until evenly colored.
06 - Frost completely cooled cakes or cupcakes with the buttercream. Garnish with edible flowers if desired and serve.