Method

1. Put the milk and lemon zest in a saucepan and bring just to a boil. Remove the pan from the heat, cover and set aside for 30 minutes so the zest can infuse the milk. Reheat the milk before mixing the custard.
2. Preheat oven to 160°C. Line the bottom of a roasting pan with a double thickness of paper towels and place 6 custard cups (approx. 1 cup capacity) in the pan. Have a fine mesh strainer lined with cheese cloth ready. Fill a stovetop kettle or saucepan with water and put it on to boil. When the water boils, turn the heat down just to keep it warm.
3. In a 1L glass measuring cup or a heatproof bowl, whisk the eggs and sugar together until well blended. Still whisking, strain in about 1/4 cup of the hot milk little by little to temper (warm) the eggs so they won’t curdle. Whisking continuously, slowly strain in the remaining milk. Discard the zest left in the strainer. Stir in the lemon extract.
4. Skim off the foam from the top of the custard with a spoon. Then divide the custard amongst the prepared cups. Carefully place the roasting pan in the oven and then pour enough hot water from the teakettle into the roasting pan to come halfway up the sides of the cups.
5. Bake for about 40-45 minutes, or until they jiggle just a little only in the very center, when you tap the cups lightly. Transfer the custards to a rack and cool to room temperature, then cover and refrigerate for at least 2 hours before serving.
6. Take custards out of the refrigerator about 15 minutes prior to serving. Serve with a dollop of fresh cream and garnish thin lemon slices.