Zest of 1 Meyer lemon

Preheat the oven to 325 F and position an oven rack in the center of the oven.

Place a sheet of parchment paper on a work surface and sift the flour, baking powder and salt onto it. Set aside.

Zest the Meyer lemons. Squeeze the juice and strain into a glass measuring cup. You should have about 1/2 cup. Add enough water to make 3/4 cup. Set aside.

Pour the sugar into the food processor and process for about 30 seconds until it is light and fine. Scoop about 1/2 cup of the processed sugar into a small container and set aside.

In the bowl of a stand mixer fitted with a whisk attachment (or if you are using a handheld mixer, in a mixing bowl), combine the remaining 1 cup sugar and the egg yolks and mix at medium speed for about 3 minutes, until it is thick, light in color and texture, and creates ribbons in the bowl when the whisk is lifted. Add the oil and vanilla bean paste, and mix until well combined.

Add 1/3 of the flour mixture and half the juice mixture, and mix to combine. Add another 1/3 of the flour mixture and the juice and zest mixture and mix to combine, and then the remaining flour, mixing to combine -- always ending with flour possible when making a cake. Pour the mixture into a large mixing bowl, scraping the bottom, and set aside.

Clean the stand mixer bowl and whisk (or detach the handheld mixer blades and clean them and the bowl) with hot soap and water and dry very well, making sure there's not even a speck of grease on anything.

Return the bowl and whisk attachment to the stand mixer (or reassemble the handheld mixer and set up the mixing bowl), add the egg whites, and mix at medium speed until they are foamy. Add the cream of tartar, and mix at medium speed until the mixture forms soft peaks. Add the remaining sugar, a little at a time, and beat the whites until they hold stiff and glossy peaks (see note).

Stir 1/3 of the whites gently into the batter to lighten it. Fold in half of the remaining whites until there are a few streaks remaining. Fold in the last of the egg whites just until mixed.

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