Peel onion and cut into thin rings. Wash the thyme, shake dry and pluck off the leaves. Heat the oil in a pan and fry the onion until golden brown. Add thyme and honey and simmer briefly.
Season with pepper and a little salt, remove from heat.
For the Harissa butter, mix 75 g butter and Harissa and season with a little salt. For the horseradish parsley butter, wash parsley, shake dry and chop finely. Mix 50 g butter, parsley and horseradish, season with a little salt.
Quarter the flat bread and cut it open horizontally. Roast the bread on the hot grill with the inside down briefly. Cut the camembert into slices.
Take flatbread off the grill. Cover 2 lower halves with camembert slices, drizzle 1 of them with pesto and cover 1 with honey onions. Place the upper halves on top and press down well. Spread the remaining 2 lower bread halves each with one type of butter, cover with the upper halves and press down well.
Roast the breads on the hot grill again on each side for about 2 minutes until crispy and cut them into pieces or strips.