Preheat oven to 350 degrees F. Line a cupcake pan with paper liners,In a medium bowl, mix together the flour, baking powder and salt. Set aside.
In the bowl of a stand mixer with the paddle attachment on, beat butter and lavender sugar until thick. Scrape down the sides as needed.
Add the eggs and mix well. Add the vanilla extract, lavender extract and lemon juice and zest, beat to combine.
Reduce speed to medium and the flour mixture in thirds, alternating with the buttermilk, make sure they are well incorporated between each addition. Scrape down the bowl and mix for another 30 seconds until the mixture is smooth.
Divide the batter evenly between the 12 cupcake liners, filling about 2/3 full.
Bake for 20 –23 minutes or until the tops spring back or a toothpick inserted in the center comes out clean. Allow to cool in the pan for 5 minutes beforetransferring to a wire rack to cool fully before frosting.
For the Lavender Buttercream
Sift the confectioners' sugar to assure there are no lumps.
With a handheld or stand mixer, beat the butter at medium speed until fluffy (approx. 2 mins.) Gradually add the sifted sugar alternating with the heavy cream, lavender and vanilla extracts. Beat on low speed after each addition. Stop adding cream when the desired consistency has been reached.
Frost cooled cupcakes and top with rainbow sprinklesas desired. Then enjoy!