Combine all ingredients except sparkling wine in a mixing glass with clean ice. Stir 30 seconds to dilute, chill and combine. Strain into a champagne flute, top with the sparkling wine and a couple more drops of bitters. Cut a coin sized piece of peel from a fresh organic lemon, squeeze the oils onto the drink, wipe the rim of the glass with the peel.
For large gatherings, scale up the recipe to desired amounts and combine gin, vermouth and pear liqueur in a pitcher ahead of time. Mix cocktails for your guests to order by pouring the mixture into a mixing glass with clean ice, adding bitters and proceeding as above. There should be room in the mixing glass to stir up several cocktails at once.