Wash and stone fresh mirabelles (drain well from the glass). Wash the fillet, dab dry and tie into shape with kitchen string. Season with salt and pepper. Halve the garlic cloves.
Wash the thyme and dab dry.
Preheat oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer). Heat the lard in an ovenproof pan. Sauté the fillet for 6-8 minutes. Add garlic and thyme and fry.
Repeatedly pour the lard from the pan over them. Place the fillet in the pan in the hot oven. 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 briefly. Wash the rosemary, dab dry and remove the needles. Add the lemon zest to the mirabelles and leave to stand briefly.
Season with salt and pepper.
Take the fillet out of the oven, wrap in aluminium foil and let it rest for about 10 minutes. Pour the roast meat into a pot, add the veal stock and boil down a little. Season to taste with salt and pepper. Cut veal fillet into slices.
Arrange caramelized mirabelles, gravy and fillet slices on plates.