Trim the leaves off and cut the beet stems into 7-8 cm (3 inch) lengths, discarding any soft or damaged areas. Keep the greens for another recipe.
Clean and scald one large (quart/liter) canning jar or two medium (pint/half liter) jars with boiling water, then set them aside. (See Quantity Note below)
Bring the vinegars, sugar, and honey to a boil in a medium pot. Add the salt, spices, cilantro (if using) and sriracha and remove from heat. Allow to cool slightly.
Pack the beet stems and sliced onions tightly in the clean jar(s) and pour the warm pickling liquid over top. Cover, then cool to room temperature and transfer to the fridge. Leave for at least one week for best flavour.
Notes
Sugar Note: I use simple granulated white sugar for this recipe, but you can use a less refined granulated cane sugar if you like.Honey Note: If you don't want to use honey, you can substitute an equal quantity of brown rice syrup or agave syrup. You can also use light maple syrup, though it does contribute a flavour of its own. If you don't want to use a syrup, you substitute with sugar. Honey is sweeter than sucrose, so you might want to add 1-2 extra tablespoons to make up the difference in flavour.Spiciness: If you’re particularly fond of a fiery hit of spice, feel free to double the amount of sriracha in this pickle recipe.Relish Option: You can finely dice the beet stems to use as a relish (drain the excess brine before serving).Quantity Note: This recipe tends to fill up a single quart/liter canning jar with some brine leftover. Because it can be difficult to exactly determine how much space the beet stems will take up, I also like to prepare a small (half pint/quarter liter) jar to accommodate any 'overflow.'