Add the whole milk into a small saucepan. Cook over medium heat, stirring frequently, until the milk begins to simmer. Remove from the heat and stir in the dried culinary lavender. Let the lavender steep in the milk for 15 minutes, then strain the milk through a fine mesh sieve set over a small bowl. Press all the excess milk out of the lavender buds before discarding them. Allow the lavender milk to cool completely before adding it to the buttercream.
In the bowl of a stand mixer fitted with the paddle attachment (a hand mixer works fine too!) cream the butter on medium-high until it’s creamy and light in color, about 5 minutes.
With the mixer on low speed, add the powdered sugar a few cups at a time, scraping down after each addition and making sure each cup is fully incorporated before adding the next one. Add the lavender milk, vanilla, salt, and food coloring (if using) and continue mixing on low speed until fully combined and smooth, scraping down the bowl and paddle as needed.
The lavender milk (from Step 1 of the recipe) can be made 2-3 days ahead and stored in an airtight container in the refrigerator. Bring it back to room temperature before adding it to the buttercream.
The lavender buttercream can be made ahead and stored in an airtight container in the refrigerator for up to two weeks. When you’re ready to use it, bring it back to room temperature and re-whip in your stand mixer to bring back to smooth buttercream consistency.
Yield: This buttercream makes enough to:
Frost 12-15 cupcakes with a piping bag
Fill and crumb coat a three-layer 6-inch cake or two-layer 8-inch cake. To have enough for frosting and decorating as well, double the recipe.