Whisk egg yolks and set aside.
In a heavy bottom saucepan, combine milk, cream, sour cream, salt and honey.
Snip individual florets into mixture, discarding as much of the stem material as possible. Heat over medium high heat until hot stirring frequently. DO NOT BOIL.
When milk/cream mixture is hot, vigorously whisk a ladle full into the egg yolks. Slowly pour egg mixture into milk/cream mixture, again whisking vigorously.
Return saucepan to medium heat and continue to cook until thickened and coats that back of a spoon, stirring constantly. Remove from heat. Stir in vanilla extract.
Pour mixture through a fine mesh sieve into a container or bowl to chill. Discard elderflower remnants.
After your cream mixture is completely chilled, follow the instructions of your ice cream maker for churning. Alternatively, if you do not have an ice cream maker, pour mixture into a rimmed baking dish and chill in freezer, scraping mixture with a fork every half hour onto solid but light in consistency.