Rabbi Rachel Barenblat saved the etrogs from last Sukkot and has been soaking them in vodka, making etrogcello to celebrate the trees.
But really the reason I make the etrogcello is so that we can drink it at Tu BiShvat. The New Year of the Trees; the birthday, according to Talmud, of every tree, no matter when it was planted. The date when (our tradition says) the sap begins to rise to feed the trees for the year to come; the time when cosmic sap begins to rise, renewing our spiritual energy for the welter of spring festivals ahead. How better to celebrate Tu BiShvat than with this pri etz hadar, this fruit of a goodly tree, which we so cherished back at Sukkot? It stitches the harvest season to this moment in deepest New England winter. It reminds me that everything which has been dormant can once again bear fruit.