Step 1

Position a rack in the lower third of your oven and preheat to 325ºF. Rub the bottom and sides of a 9-inch springform pan or cake pan with the coconut oil. Line the bottom of the pan with a round of parchment paper, and rub the parchment with coconut oil as well. If using a springform pan, place on a rimmed baking sheet to catch any drips.

Step 2

In a large bowl, whisk together the olive oil, ½ cup (100 g) sugar, lemon zest and juice, and egg yolks to combine. Place a mesh strainer over the top and sift in the almond and tapioca flours, baking powder, and salt. Stir to combine.

Step 3

Place the egg whites and cream of tartar in the clean bowl of a stand mixer fitted with the whip attachment (or use a large bowl and electric egg beater). Whip on medium-high speed until foamy, 30-60 seconds. With the mixer running, gradually sprinkle in the remaining ¼ cup (50 g) sugar, 20-30 seconds. Continue to whip until the egg whites are shiny and hold firm peaks when you lift the whip out and hold it upside-down, 2-4 minutes.

Step 4

Use a large flexible silicone spatula to fold one-third of the whipped egg whites into the batter until just combined. Fold in the remaining egg whites until just combined and no streaks remain. Scrape the batter into the prepared pan and smooth the top.

Step 5

Bake the cake until deep golden on top, beginning to pull away from the sides of the pan, and the top springs back when pressed lightly, 40-45 minutes. If the cake is darkening too quickly, tent the top with a piece of aluminum foil. Let the cake cool slightly, then loosen the edges with a small, offset spatula and release the sides if using a springform pan. Invert the cake onto the wire rack and peel away the parchment, then turn right side up and let cool completely. Dust with powdered sugar if using, cut into wedges, and serve with cream and berries if you like. The cake keeps well airtight at cool room temperature for 1 day or refrigerated for up to 4 days.