These can be left to soak up the sauce before being reheated in the oven later on in the evening.
*This recipe makes 12.
1. Preheat the oven to 140°C/ gas mark 1.
2. First make the sauce by whisking the crème fraîche with the egg. Stir in the grated Gruyère and season with a pinch of grated nutmeg and ground white pepper.
3. Cut the bread into 24 slices in total. Lightly toast one side of the bread and lightly butter the other side. Spread generously with mustard, then top with a slice of ham, a slice of Gruyère and a spoonful of the sauce. Top the sandwich with another slice of bread, toasted side up. Repeat for all 12 sandwiches.
4. Line one or two baking trays with non-stick baking paper. Using a sharp knife, cut each sandwich into 3cm-wide fingers. Arrange the fingers on the lined trays, then pour over the remaining sauce and top with grated Emmental.
5. Bake in the oven for 30 minutes if you want the croques to still be quite moist or all the way up to 1 hour 30 minutes for a crisp croque with a concentrated flavour.
6. Serve on a large wooden board or platter and garnish with fresh thyme sprigs.
TIP: You could swap the baked ham in these mini croque monsieurs for serrano ham or serve plates of garlic-coated salami, chorizo pamplona and pepper-coated salami on the side.