Fill a bowl with water and soak the elderflowers in it. Carefully shake out the dust under water. Put the flowers on kitchen paper and let them dry well.
Mix flour, milk, sugar, salt and eggs until a homogeneous, liquid batter is formed. Let rest for 20 minutes.
Heat oil in a deep frying pan until very hot. Pull the elderflowers through the batter, fry them out in the oil and drain the fat on a layer of kitchen paper.
Sprinkle the flowers with powdered sugar before serving.