Put elderberries into a quart Mason jar and pour over the vodka. Add the lemon rind (make sure the rind has no white pith, as it is bitter.) Seal and put in a dark cupboard for at least a month, or up to a year.
The alcohol will extract flavor from the elderberries over time, so the longer you let it sit, the inkier it will get.
When it is the color you want -- anything from a Pinot Noir color to downright black -- pour the vodka through a strainer lined with cheesecloth into another jar and add sugar.
How much sugar or honey? At least 2 tablespoons, but to your taste. Shake to combine and put back in the cupboard. After a few days or weeks, the sugar will completely dissolve and the elderberry liqueur is ready to drink. It keeps forever.
Notes
Any sweetener you like will work here, but white sugar has the most neutral flavor.