1. Preheat the oven to 425°F (220°C).

2. In a large bowl, combine 1 cup all-purpose flour and 2 cups milk, mixing until smooth.

3. Add 2 eggs and 1/4 teaspoon salt, then pour in the remaining 1 cup milk and whisk until fully blended.

4. Butter a 12-inch ovenproof skillet or 9-inch round cake pan.

5. Pour the batter into the skillet, then arrange the sliced apples evenly on top.

6. Bake for 25 minutes until the edges are puffed and deeply golden brown.

7. While the pancake bakes, prepare the lingonberry-onion topping (if using):

8. In a small saucepan, combine lingonberries (or cranberries), chopped onion, sugar, and salt.

9. Cook over medium heat, stirring occasionally, until the berries have burst and the onion is softened, about 10 minutes.

10. Stir in 1 tablespoon butter until melted.

11. Remove the pancake from the oven and let it rest for 5 minutes.

12. Serve warm, topped with the lingonberry-onion mixture, if desired.