How to Make It
Preheat the oven to 350°. Butter a 2-quart baking dish.
In a large saucepan, combine the oats, milk, turbinado sugar and salt and bring to a simmer. Cook over moderate heat, stirring occasionally, until thickened to a porridge consistency, about 15 minutes. Remove from the heat; let cool slightly.
Working quickly, stir the egg yolks into the oatmeal until well blended. Fold in 1 cup of the berries and the lemon zest.
In a large bowl, using a hand mixer, beat the egg whites at medium speed until medium-stiff peaks form, about 3 minutes. Gently fold the whites into the oatmeal just until combined. Scrape the mixture into the prepared dish and bake for about 30 minutes, until golden and puffed. Dust with confectioners’ sugar and serve hot with the remaining 1 cup of berries and maple syrup, if desired.