01 - Preheat oven to 350°F. Grease and flour a 9-inch round cake pan or line with parchment paper.
02 - Whisk together flour, baking powder, baking soda, salt, and chopped lavender in a medium bowl. Set aside.
03 - Combine sugar and lemon zest in a large bowl. Rub together with fingers to release essential oils.
04 - Add softened butter to sugar mixture. Beat until light and fluffy, approximately 3 minutes.
05 - Beat in eggs one at a time until fully incorporated. Add vanilla extract and mix to combine.
06 - Alternate adding dry ingredients and milk to wet mixture, beginning and ending with dry ingredients. Mix in lemon juice until just combined. Avoid overmixing.
07 - Pour batter into prepared pan and smooth top. Bake for 30–35 minutes until toothpick inserted in center comes out clean.
08 - Let cake cool in pan for 10 minutes. Turn out onto wire rack to cool completely.
09 - Whisk powdered sugar with lemon juice until smooth and pourable. Drizzle over cooled cake.
10 - Sprinkle additional lavender over top if desired. Slice and serve.