For the cake: Preheat oven to 350°F (180°C). Position rack in center of oven. Oil two 9-inch cake pans and dust with flour; set aside.
In a medium mixing bowl combine oil and sugar.
Add eggs and beat with an electric mixer at medium speed for one minute.
Add flour, salt, baking powder, dairy-free milk, lemon extract, and lemon zest; beat at medium speed for one minute.
Spoon batter evenly into cake pans. Bake for 28-32 minutes or until the centers springs back when touched and the centers are set. The time may vary on your elevation and oven temperature accuracy.
Remove from the oven and let cool in the pan on the rack for five minutes. Run a rubber spatula along the edges of each cake to loosen them. Invert onto the cooking rack.
For the frosting: In a medium mixing bowl, beat butter smooth and creamy.
Gradually add powdered sugar, one cup at a time, beating well. Alternate one cup of powdered sugar and 1 tablespoon of lemon juice until all ingredients are blended.
Beat in additional lemon juice if needed to obtain desired constancy.
Place on cake, dome side down, on a plate or cake platter. Spread a ¼ inch layer of frosting on it. Spoon lemon curd into the center and spread until it’s a half inch from the edges.
Add second cake to the top and frost the sides and tops. Tip: I like to put frosting in a piping bag and pipe in on, then spread it. It helps eliminate crumbs getting mixed into the frosting and adds the right amount of frosting.