Meanwhile, finely grate the zest of one of the lemons; set aside. Cut a thick slice off both ends of the zested lemon to expose the flesh. Stand the fruit upright, then cutting from the top down, remove the peel, including all the white pith. Holding the fruit over a bowl
to catch the juice, use a paring knife
to cut along either side of each segment to free it from the membranes; let each segment fall into the bowl as you go. Once you've removed all the segments, squeeze any juice from the membranes into the bowl and then discard. Remove the seeds and set the segments aside in another small dish. Measure the juice in the bowl. Cut the remaining lemon in half and squeeze to obtain 2 tablespoons juice total.