This amazing pudding sets from the acid in the lemon juice; there's no need to add gelatin. The texture is best when the puddings are allowed to firm up overnight.
Peel the zest in strips from the lemons. Cut the strips into 1-by-1/8-inch julienne. Transfer the zest to a large saucepan and cover with water. Bring to a boil and simmer for 10 minutes. Drain and return the zest to the saucepan. Add 1 1/4 cups of the sugar and 1 1/4 cups of water and bring to a boil. Simmer over moderate heat until the syrup is reduced to 2/3 cup and the zest strips are translucent, about 10 minutes. Using a slotted spoon, transfer the strips to a bowl and toss with the remaining 1 cup of sugar. Let cool.
Add 3 cups of the cream to the lemon syrup in the saucepan and simmer until reduced to 3 1/2 cups, about 15 minutes.
Halve and juice the lemons; you should have 3/4 cup of juice. Add the lemon juice and salt to the saucepan and let cool slightly. Pour the pudding into 6 glasses and chill until set; at least 5 hours and preferably overnight.
Beat the remaining 1/2 cup of cream until soft peaks form; dollop on the puddings. Garnish with the zests and serve.