Preheat the oven to 375°F (190°C). Grease and line a round cake pan.
In a bowl, mix flour, sugar, and oats. Rub in the cold butter with your fingers until crumbly. Refrigerate until ready to use.
½ cup sugar, ¼ cup old-fashioned rolled oats, 6 tablespoons unsalted butter, ¾ cup all-purpose flour
In a large bowl, beat butter and sugar until light and fluffy. Add eggs one at a time, mixing well after each.
2 large eggs, ½ cup sugar, ½ cup unsalted butter
In a separate bowl, whisk flour, baking powder, cinnamon, and salt. Fold into the butter mixture, then stir in the heavy cream.
3 tablespoons heavy cream, 1 teaspoon baking powder, 1 teaspoon ground cinnamon, ⅛ teaspoon salt, 1 ¼ cups all-purpose flour
Spread the batter evenly in the pan. Arrange apple slices on top and sprinkle with the streusel.
3 Granny Smith apples
Bake for 50 to 60 minutes, until golden and a toothpick inserted in the center comes out clean.
Let cool slightly, then dust with confectioners’ sugar before serving.
Confectioners’ sugar