Place the beets in a large pot and add enough water just to cover. Bring to a boil over medium-high heat. Cover and reduce the heat to medium-low. Cook for 30 to 40 minutes. Remove the beets from the water and let rest until cool enough to handle.  Using a paper towel, rub the beets all over to remove their skins. Cut the beets into wedges and divide them between two pint-sized canning jars, leaving 1-inch of space at the top of the jar. Add the dill sprigs. In a medium saucepan, combine the vinegar, sugar, salt, garlic, peppercorns, mustard seeds and 1½ cups of water. Bring to a boil over medium-high heat and stir well to dissolve the sugar. Remove from the heat immediately and pour over the beets, stopping at ½ inch from the rim of the jar. Cover the jars and let cool to room temperature. Transfer to the refrigerator to cool completely.