A tender, vanilla-forward cake enriched with the nutty sweetness and hearty texture of freshly milled whole wheat, finished beautifully with a fluffy vanilla buttercream.
Preheat oven to 350°F (175°C). Grease or line two 8-inch round pans or a 9×13-inch pan. In a saucepan, heat the butter with the milk until the butter melts; set aside to cool slightly.
In a stand mixer fitted with the whisk, add the eggs. Start on low, then increase to high and whip 1 minute.
Slowly add the sugar and whip until pale, light, and fluffy, about 5 minutes. Mix in the vanilla extract and oil.
In a separate bowl, whisk together the whole wheat flour, baking soda, baking powder, and salt.
With the mixer on low, alternate adding the milk–butter mixture and the dry ingredients to the whipped eggs. Mix just until combined. Let the batter rest 5–10 minutes, then gently fold a few times.
Pour batter into the prepared pan(s). Bake 25–30 minutes for two 8-inch rounds or 35–40 minutes for a 9×13, until golden and a tester comes out clean. The center should not wobble. Cool on a rack.
Make the vanilla buttercream: In a clean mixer bowl, beat the room-temperature butter until smooth. Add powdered sugar and mix on low to combine, then whip on high until fluffy. Add heavy cream, salt, and vanilla; whip 1–2 minutes more.
Frost the cake once completely cooled and serve.