Preheat oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). Line a tray with baking paper.
Wash 4 stems of thyme, shake dry. Wash 2 organic lemons hot, dry, cut 1 into slices. Cut 1 ready-to-cook chicken (1.2 kg) into 10 pieces, wash, dab dry. Season with salt and pepper. Put the chicken parts, thyme and lemon slices on a baking tray.
Fry in a hot oven for about 50 minutes. Grate half the peel of the other lemon, squeeze the fruit. Mix the zest, juice, 2 tablespoons of grainy mustard, 2 tablespoons of brown sugar and 4 tablespoons of olive oil. Spread the chicken with it after about 30 minutes roasting time. Repeat from time to time until the sauce is used up.