Peel the onion and cut into thin rings. Sauté the onion in oil, thyme and honey and let simmer. Season with salt and pepper and remove from the heat.
Mix 75g butter with the harissa and fold in a little salt.
Mix 50g butter with the parsley and the horseradish.
Divide the flatbread into quarters and heat briefly on the contact grill. Top each with camembert and brush with pesto then spread 1 tablespoon of the honeydew onion on top.
Spread the butter on the other sides and fold everything up.
Cook in the contact grill for 2 minutes until nice grill marks form.
This website provides approximate nutrition information for convenience and as a courtesy only. Nutrition data is gathered primarily from the Spoonacular Database, whenever available, or otherwise other online calculators.