To prepare a st patricks day green velvet layer cake recipe, first preheat the oven to 350 degrees F (180 degrees C). Grease and flour two 8-inch round cake pans and set aside. Cream the butter and sugar on medium speed until light and fluffy, about 2 minutes. Add the eggs and vanilla and beat until combined. Gradually beat in the flour mixture, scraping down the sides of the bowl as needed. Pour the batter into the greased pan and bake for 35 to 40 minutes, or until toothpick inserted in center comes out clean. Let cake cool in pan for 10 minutes before removing to wire rack to cool completely.