- 2 1/2 cups unbleached all-purpose flour, divided
- 2 tsp baking powder
- 1 tsp fine sea salt
- 1 cup (2 sticks) unsalted butter, at room temperature
- 1/4 cup vegetable oil
- 1 3/4 cups granulated sugar
- Zest of 1 lemon
- 3 large eggs, at room temperature
- 1 tsp vanilla extract
- 3/4 cup buttermilk
- 3 cups mixed berries, such as blackberries, raspberries, and blueberries
- 1/2 cup (1 stick) unsalted butter, at room temperature
- 2 cups powdered sugar
- Fresh lemon zest
- 2 Tbsp fresh lemon juice
- Pinch of salt
Preheat oven to 350°. Generously butter a Bundt pan.
In a medium bowl, whisk or sift 2 1/2 cups minus 2 tablespoons flour, baking powder, and salt together and set aside.
In the bowl of a stand mixer with the paddle attachment, cream together butter, sugar, oil, and lemon zest until light and fluffy, 3-5 minutes. With mixer on low speed, add eggs, one at a time, scraping down bowl between each addition. Add vanilla and beat to combine.
Add 1/3 flour mixture to batter, slowly mixing until just combined. Add half of buttermilk, another 1/3 of flour mixture, remaining buttermilk and remaining 1/3 of flour mixture. Turn off machine and, using a large spatula, finishing combining batter.
In a small bowl, toss berries with reserved 2 tablespoons flour. Gently fold berries into cake batter. Spoon batter into prepared baking pan and spread evenly. Bake, rotating the cake 180° after 30 minutes, until a tester inserted into center of cake comes out clean, 55-60 minutes.
Transfer to a wire rack to cool, about 30 minutes. Invert, remove from Bundt pan and let cool completely.
Using a stand mixer with the paddle attachment, whip butter until light and fluffy, 1-2 minutes. Add powdered sugar, lemon zest, lemon juice, and salt. Mix on low speed until combined. Increase speed to medium-high and whip for 3 minutes. Pipe buttercream over cake.