Wash, hull and stone the yellow plums. Wash the meat, dab dry and season with salt and pepper. Tie the fillet into shape with kitchen string. Cut garlic cloves in half. Wash thyme and dab dry.
Melt the clarified butter in an ovenproof pan. Sauté the veal fillet for 6-8 minutes, repeatedly pouring the clarified butter over it. Place the pan in the preheated oven (electric range: 175 °C/ convection oven: 150 °C/ gas: level 2).
Cook the fillet for about 10 minutes. In the meantime melt butter in a pan. Add the mirabelles and toss in. Sprinkle with sugar and caramelise the mirabelles. Wash the rosemary, dab dry and pluck roughly.
Add the rosemary and lemon zest to the mirabelles, toss through or allow to draw briefly. Season with salt and pepper. Take the fillet out of the oven, wrap in aluminium foil and let it rest. Pour the roasting mixture into a pot, add veal stock and let it boil down a little.
Season to taste with salt and pepper. Cut the fillet into slices. Arrange caramelized mirabelles, gravy and fillet slices on plates. Garnish with thyme.