Cut the chicken breast fillets lengthwise. Wash and dry them. Sprinkle both sides with lemon juice.
Roughly dice the toast and cheese, then chop them together in a blender until crumbly.
Heat the clarified butter over medium-high heat in a skillet. Fry the chicken fillets for 30 seconds on each side to sear them. Transfer to an ovenproof dish.
Sprinkle the lemon zest over the chicken. Spread the bread and cheese crumbs evenly over the top. Spoon the crème fraîche over the surface, then top with small flakes of butter.
Bake in a preheated oven at 220°C (428°F) with top and bottom heat for 15-20 minutes until the chicken reaches 74°C / 165°F in the thickest part and is golden brown.