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.

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.

Place the egg whites and cream of tartar in the clean bowl of a stand mixer fitted with the whip attachment.

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, 2-4 minutes.

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.

Bake the cake until deep golden on top, about 40-45 minutes.

Let the cake cool slightly, then loosen the edges 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 and cut into wedges.