In a large bowl, beat the butter and sugar together using an electric mixer until light and fluffy, about 5 minutes. Beat in the eggs one at a time; add the vanilla.
In another large bowl, whisk together the flours, baking powder and salt. With mixer on low, add half the flour mixture to the butter and egg mixture and beat until just combined. Add the buttermilk and mix well to combine. Add the remaining flour mixture and beat until just combined, scraping down the bowl as necessary.
Pour batter into the prepared pans, place in the oven and bake for about 45 minutes, until a tester inserted in the middle of the cake comes out clean. Remove from oven and place on a rack to cool for 15 minutes, then turn the cake out onto the rack to cool completely.
We used a simple buttercream frosting — 1 cup butter, at room temperature/softened, 3 ½ cups confectioners sugar, 1 teaspoon vanilla, 3-4 tablespoons milk, and Elsie’s choice of food coloring — but this would be gorgeous with a chocolate ganache or even a maple-cream cheese frosting.