1. Stir the butter using a kitchen mixer to make the tart pastry. Slowly add sugar, powdered sugar, walnuts and salt. Fold in egg, carefully add flour and work everything into a smooth dough. Make a ball, wrap in plastic wrap and chill in the refrigerator overnight.
2. Place the dough on a lightly floured surface and roll it out evenly, then place it in a tart pan that is 28 cm in diameter. Press the edges with your fingers and trim off the dough that hangs down using a knife.
3. Wash and halve apples. Slice apples into thin slivers.
4. Preheat the oven to 190 degrees upper/lower (convection oven to 175 degrees). Arrange the apple slivers like a wreath on the pastry dough.
5. To make the glaze, whisk the sugar with the eggs, cream and lemon zest in a bowl. Spread over the apples evenly. Place in the oven and bake about 35-40 minutes.