Preheat the oven to 400°F (200°C).

Grease an oven-safe serving dish.

Heat the oil in a frying pan.

Fry the sausages, turning occasionally, until browned on all sides.

Remove the sausages from the pan and drain on paper towels to remove excess grease.

In a bowl, whisk together the whipping cream and eggs until well combined.

Stir in the finely chopped marjoram and freshly grated nutmeg.

Season the cream mixture to taste with salt and pepper.

Slice the browned sausages into smaller pieces.

In the prepared baking dish, arrange the sliced sausages, thinly sliced French bread, and apple wedges.

Pour the cream and egg mixture evenly over the sausage, bread, and apples.

Sprinkle the grated Gruyere cheese and flaked hazelnuts over the top of the mixture.

Bake in the preheated oven for 35-40 minutes, or until the cheese is golden brown and bubbling.

Remove from the oven and let it cool slightly before serving.

Garnish with the reserved marjoram sprigs before serving.