Place the elderflower umbels in a bowl of water, gently rocking them back and forth to remove the dust. Spread out on a towel to dry. If the flowers are still wet, they will not accept the batter later.
Whisk the flour, milk, rum, salt, honey and egg into a liquid batter. Let stand for 30 minutes to soak. Heat the fat to 180 degrees in a deep fryer or a shallow saucepan. It`s hot enough when small bubbles appear on a wooden spoon stick dipped into it. If necessary, check the temperature with a few drops of the dough. Dip the elderflower umbels in the batter and fry them one after the other until golden yellow in the hot fat. Drain on paper towels. Mix the cinnamon and sugar and serve the flowers sprinkled with cinnamon sugar.
Elder flowers can be found in gardens, parks and on the edges of fields from mid-May to June, depending on the weather. It is better not to collect at the roadside, there are too much exhaust gases in the air. Cut off the flowers with scissors and leave a piece of the stem on the flower. This will make it easier to dip them into the batter later.