Preheat the oven to 180°C (approximately 350°F).
Rinse the apples, halve and remove the cores. Slice the apples and sprinkle with lemon juice. Separate the eggs, beat the egg whites and salt until very stiff. Beat the egg yolks with the sugar until fluffy. Mix the flour, cornstarch, and ground walnuts and mix alternating with the milk and the cream into the yolk mixture until smooth. Fold in the egg whites. Butter a tart pan and line it with the apple slices. Evenly spread the dough over the apples and bake until golden brown, about 30 minutes. Serve dusted with powdered sugar.