Lemon Vanilla Cupcakes

Name: Lemon Vanilla Cupcakes
Ingredients: 1 cup superfine sweet rice flour; 1 cup millet flour; 1/2 cup sorghum flour; 1/2 cup cornstarch; 1/2 teaspoon xanthan gum; 2 teaspoons baking powder; 1/4 teaspoon salt; 6 tablespoons unsalted butter, at room temperature; 6 tablespoons coconut oil (solid stage preferably); 2 1/2 cups sugar, divided; 1 teaspoon vanilla extract; 1 1/4 cups milk; 6 egg whites (use the yolks in the buttercream); zest of 2 lemons; 1/2 cup (125ml) lemon juice; 1/4 cup sucanat (or sugar); 1 egg + 1 egg yolk; 4 tablespoons unsalted butter, at room temperature; 6 egg yolks; 1 cup sugar; 1/2 cup water; 3 sticks unsalted butter, at room temperature; 1/2 vanilla bean