1. In a large bowl, with an electric mixer, beat the eggs until they are foamy. Add the sugar in a stream, beating constantly. Beat the mixture for 3 minutes, or until it is thick and pale.
2. In the top of a double boiler set over boiling water, whisk together the egg mixture, lemon zest, lemon juice, water and salt. Cook the mixture, whisking, for 10 minutes, or until the sauce thickens around the edge.
3. Transfer the sauce to a bowl and let it cool to room temperature. Serve with warm gingerbread.