Preheat oven to 350°F. Line a cupcake pan with 12 cupcake liners.
Place the lavender and milk in a blender and blend for or pulse a few seconds to blend the lavender into small bits.
Whisk the cake flour, baking powder, baking soda, and salt in a medium bowl.
In the bowl of a stand mixer with the paddle attachment, or large bowl with electric mixer, beat butter and sugar on high speed to cream for 2 minutes, until light and fluffy. Scrape down the bottom and sides of the bowl. Add the egg whites, vanilla extract, lavender extract and vanilla beans and beat on medium-high speed until smooth and combined, at least 2 minutes. Beat in the greek yogurt or sour cream and scrape down the bottom and sides of the bowl.
With the mixer running on low speed, gradually add the dry ingredients until just incorporated. Pour in the lavender milk with the mixer running on low until just combined, being careful not to over mix.
Fill each prepared muffin cup 2/3 of the way full. Bake in the preheated oven for 18-22 minutes, or until a toothpick inserted in the center comes out clean. Cool cupcakes completely before frosting.
To make the frosting, place room temperature butter in a large bowl and beat with an electric mixer until smooth, about 3 minutes. Sift in powdered sugar and add heavy cream, honey, lemon zest, salt, and optional food coloring. Beat until combined and no lumps remain, about 3 more minutes.
Pipe frosting onto cupcakes using a piping bag or plastic bag with the tip cut off (I used Wilton 1A tip). Garnish with additional lavender or edible flowers if desired.