Place the spinach in a large pan, cover and wilt over a medium heat then drain. Heat the butter in the same pan and sauté the onion. Remove the pan from the heat, stir in the spinach and season. Place the cake dough on the prepared oven tray. Top with half the cheese slices. Distribute the spinach on top. Combine the eggs and cream, season and pour over.
Bake for approx. 30 mins. in the lower half of an oven preheated to 200°C. Remove and place the remaining slices of cheese on top. Drizzle with honey and scatter with rosemary. Finish off in the oven for approx. 20 mins. Total baking time: approx. 50 mins.