How to Make It
In a medium saucepan, bring 2 inches of water to a boil; keep the water at a simmer over low heat. In a large stainless steel or glass bowl, using your fingers, rub the lemon zest into the sugar. Whisk in the lemon juice, eggs, egg yolk and a pinch of salt. Set the bowl over the simmering water and cook the mixture, stirring, until very thick, 5 to 7 minutes. Scrape the cream into a medium bowl.
Add 3 tablespoons of the butter to the cream. Using an immersion blender, puree until the cream is smooth. Add the remaining butter and puree until incorporated. Press a sheet of plastic wrap directly onto the surface of the cream and refrigerate until well chilled, about 4 hours. Spoon over fresh berries and serve.