Wash the lemons in hot water and dry them. Cut off the upper third as a lid. Carefully squeeze the lid and lemons. For the syrup 1⁄2 measure out l lemon juice. Bring to the boil with butter and 175 g sugar and boil down to approx. 300 ml.
Remove from heat and let it cool down.
Meanwhile, carefully scrape the remaining pulp out of the lemons and lids with a teaspoon and a small knife. Cut the undersides of the lemons straight so that they do not tip over.
Separate eggs. Whip egg whites and cream separately until stiff. Whisk the egg yolks and 75 g sugar with the whisks of the mixer until white-creamy. Stir in lemon syrup. Fold in the cream first, then the beaten egg white.
Spread the mixture into the lemons. Cover lemons and lid with foil and freeze for at least 3 hours. Remove everything. Put the lid on the lemons. Let thaw for 10-20 minutes, then serve.