Heat the oven to 190 C / 375 F. Lightly butter a 20 x 28 cm (8 x 11 inch) baking dish.

Toss the sliced apples with 1 tsp cinnamon, 1 tbsp maple syrup, and lemon juice in a bowl until coated. Arrange the slices in an even layer across the bottom of the prepared baking dish.

Whisk together the oats, cardamom, 0.5 tsp cinnamon, baking powder, and salt in a large bowl until combined.

Gently warm the milk in a small saucepan over low heat until just lukewarm, about 40 C / 100 F. Remove from heat.

Whisk the eggs, 3 tbsp maple syrup, and vanilla extract into the warm milk until smooth.

Pour the milk mixture over the oat mixture and stir until all the oats are moistened. Let it sit for 2 minutes.

Pour the oat mixture evenly over the apple layer. Press gently with the back of a spoon to flatten the surface.

Scatter the cold butter cubes evenly across the top.

Bake for 35 minutes until the edges are golden and set and the center has just a slight jiggle when you shake the dish gently.

Remove from the oven and rest for 5 minutes before scooping into bowls. Serve warm with skyr or yogurt and a drizzle of maple syrup.