Wash the lemons with hot water and dry them. Peel off the peel thinly, making sure that no white bottom peel is removed.
Bring the lemon peel to the boil in a saucepan with 1 liter of water. Halve the lemons, squeeze out the juice and pass through a fine sieve into a large bowl. Add the sugar and citric acid to the lemon juice, and pour the strained peel sauce over the whole thing. Now stir the mixture with a whisk until the sugar has completely dissolved.
Pour into the prepared - preferably dark - bottles and close them tightly.
Use: Pour approx. 1 cm of the lemon syrup into a glass together with a few ice cubes and fill up with mineral water. Tastes better than any lemonade you buy and is incredibly refreshing in summer!