From Marie Viljoen, author of "Forage, Harvest, Feast!" Find her on IG at @66SquareFeet. Marie's version of the recipe includes instructions on how to make Common Milkweed vinegar, but you'll have to buy her book to get those recipes. :)
Use scissors to snip all the milkweed flowers from the tiny stems within the umbel.
Combine the flwoers, sugar, water, and lemon peel (if using) in a clean jar. Stir well to dissolve the sugar. Cover the jar's mouth with a layer of cheesecloth secured with a rubber band or string. You want to keep insects out and let air in.
Leave the jar at room temperature for about 3-6 days. Stir every day until you bottle the cordial. For the first day or three you may notice no change. But bubbles will form as fermentation becomse acive, and you will hear a fizzing when you put your ear to the jar's mouth. The flowers will also rise in the jar as gas pushes them up. Push them down again with a clean spoon.
When it is extremely fizzy, give the cordial one more day. Strain the liquid through a fine-mesh sieve into a clean bowl. Strain again through a double layer of cheesecloth. (I use a coffee filter!)
Pour the strained cordial into clean bottles. Store in the fridge where it will keep indefinitely.