Center a rack in the oven, and heat it to 350. Generously butter a 10-inch tube pan (or use a Bundt pan with minimal crannies), dust the interior with flour and tap out the excess. Be assiduous — this cake is a sticker. Alternatively, use baker’s spray.

Whisk together the flour, baking powder and 1/4 teaspoon of the salt; set aside.

Using a mixer with a whisk attachment, beat the egg whites and the remaining 1/4 teaspoon salt on medium-high speed until they form firm, glossy peaks. (If you’re using a stand mixer, scrape the whites into another bowl. No need to rinse the mixer bowl.)

Fit the mixer with the paddle attachment. Put the sugar and lemon zest in the mixer/mixing bowl, and rub them together until the mixture is fragrant. Add the yolks, and beat on medium speed for 3 minutes, scraping the bowl as needed — the batter will be thick, pale and shiny. With the mixer on medium, pour in the oil and continue to beat for another 3 minutes. Mix in the lemon juice, vanilla and lemon oil, if using, then scrape the bowl well. Turn off the mixer, add the dry ingredients and pulse

Beat the whites briskly with a whisk (to re stiffen them and incorporate any liquid in the bowl), and scrape a few spoonfuls over the batter. Use a flexible spatula to stir them in and lighten the batter. Turn the rest of the whites into the bowl, and fold them in gingerly. If you’re using the berries, gently fold them in just before the whites are fully incorporated. Scrape the batter into the pan, and level the top.

Bake the cake for 45 to 50 minutes, until lightly browned; a tester inserted deep into the cake should come out clean. Transfer to a rack, and wait 5 minutes. Run a blunt knife around the edges of the pan to loosen the cake (if possible — it’s not easy with a Bundt), invert onto the rack and unmold. Cool to room temperature. Dust with confectioners’ sugar, if you like.