Heat the oven to 180 C / 355 F.

Place 115 g butter for the batter in a small saucepan over medium heat. Cook, swirling often, for 4 to 5 minutes until the butter foams, then turns golden and smells nutty. Pour into a bowl immediately and set aside to cool slightly.

In a 10-inch cast iron skillet over medium heat, melt 60 g butter. Add 100 g dark brown sugar and stir until dissolved, about 1 minute.

Pour in 60 ml heavy cream and add a pinch of salt. Stir constantly for 2 minutes until the toffee bubbles and thickens slightly. Remove from heat.

Sprinkle 0.5 tsp cinnamon over the toffee. Arrange apple slices in a single overlapping layer directly on top of the toffee. Set aside.

In a large mixing bowl, whisk together 180 g flour, 130 g dark brown sugar, 1.5 tsp baking powder, 1 tsp cinnamon, 0.5 tsp ginger, and 0.25 tsp salt.

In a separate bowl, whisk the 2 eggs, 120 ml milk, and 1 tsp vanilla until combined. Pour in the cooled brown butter and whisk again.

Add the wet ingredients to the dry ingredients and stir with a wooden spoon until just combined. A few lumps are fine - do not overmix.

Spoon the batter evenly over the apple layer in the skillet. Spread gently with a spatula to cover the apples without disturbing them.

Bake on the middle rack for 22 to 25 minutes until the top is golden and a toothpick inserted in the center comes out clean.

Remove from the oven and rest in the skillet for 8 to 10 minutes. Run a knife around the edge, then invert onto a serving plate in one confident motion. Serve warm.