01 - Preheat oven to 350°F. Grease and line three 8-inch round cake pans with parchment paper.
02 - Heat the milk in a small saucepan until steaming but not boiling. Remove from heat. Add Earl Grey tea bags and lavender, cover, and steep for 15 minutes. Strain and cool to room temperature.
03 - Whisk together flour, baking powder, and salt in a bowl.
04 - Beat butter and sugar with an electric mixer until light and fluffy, about 3-4 minutes.
05 - Beat in eggs one at a time, mixing well after each addition. Add vanilla extract.
06 - With mixer on low, add flour mixture in three parts, alternating with cooled tea-infused milk, beginning and ending with flour. Mix until just combined.
07 - Divide batter evenly among prepared pans. Smooth tops with spatula. Bake for 25-30 minutes, until a toothpick inserted into center comes out clean.
08 - Let cakes cool in pans for 10 minutes, then turn out onto wire racks to cool completely.
09 - Beat butter until creamy. Gradually add powdered sugar, milk, vanilla bean paste, and salt. Beat until fluffy and smooth.
10 - Place one cake layer on serving plate. Spread with frosting. Repeat with remaining layers. Frost top and sides of cake. Decorate with dried lavender buds and lemon zest if desired.