Pick flowers on a sunny day, only on undug meadow. Shake out the flowers, pluck out the yellow leaves, put them in a sieve and rinse.
Bring to a boil with the water and the lemon slices. Steep for 25 minutes with the lid closed. Pour through a gauze or a very fine sieve.
Boil the decoction and sugar openly at low temperature to syrup thickness and fill into a clean, dry bottle.
Store in a cool, dark place for about 8 months.