Cut away all of the veins, tendons, and the light-colored fat at the top of the heart and clear the ventricles of clotted blood.
Then cut the meat into slices about half a centimeter thick. Put the thyme and garlic in a freezer bag, knead and chill for 24 hours.
Then wash the pieces of meat, pat dry and fry them in a hot pan for a few seconds on each side - they should still be slightly pink when cut. Season with salt, pepper and a small pinch of sugar.