1. Preheat the oven to 325°F Bake Mode with a rack set at position “3.”
2. Spray eight 8-ounce custard cups with nonstick cooking spray and dust with 2 teaspoons of sugar each.
3. In a medium bowl, whisk together the 1⅓ cups sugar, egg yolks, buttermilk, lemon juice, and zest.
4. Sift together the flour and kosher salt, and whisk into the buttermilk and egg mixture.
5. Whip the egg whites to soft peaks, and combine the two mixtures by gently folding in the egg whites.
6. Divide the batter evenly between the custard cups.
7. Place ramekins into two 9-by-13 inch pans and fill with hot water halfway up the side of the ramekins.
8. Place the pans side by side into the oven and bake in a hot water bath for about 35–40 minutes or until the tops are lightly golden brown and the cake tops spring back when gently pressed.
9. Allow cakes to cool for 5 minutes before removing them from the water.
10. Allow the ramekins to cool, then wrap and store in the refrigerator for at least 3 hours or overnight.
11. To unmold the cake, run a butter knife gently around the edges of the cakes.
12. Place a plate over the ramekin, turn upside down and gently shake to release the cake.
13. Optionally, top with whipped cream and fresh berries.