- Preheat the oven to 350°F.
- In a large bowl, with an electric mixer on medium speed, cream the butter and sugar until fluffy.
- Add the egg yolks, one at a time.
- Add the lemon zest, lemon juice, and flour, stirring until just barely combined.
- Stir in the milk and cream until smooth.
- In a separate large bowl, beat the egg whites, until they hold soft-to-medium peaks, adding the salt halfway through.
- Fold into the custard mixture.
- Pour the custard mixture into a 10-inch round cake pan and set into a larger pan filled with 1-inch water.
- Bake for about 50 minutes, or until the custard is just set.
- Let cool to room temperature.
- Serve on a plate or in a glass bowls, garnished with mint leaves or berries.