Remove zest from the lemons and juice them. Reserve 9 grams of the zest and 90 grams of the lemon juice.
Whisk the juice, zest, eggs, salt and first sugar (100g) until smooth.
Quarter the lemon shells and then thinly slice.
Place the lemon strips into a pan, cover with water, bring to a boil and cook for 3 minutes.
Drain and pat dry.
Place strips and remaining sugar (50g) in a pan and cook over medium high heat, stirring constantly, until caramelized. Let cool for 2 minutes.
Combine caramelized strips and lemon juice mixture in a pan. Cook on low heat until thickened. Remove from heat and stir in butter. Allow to cool before use.