Make a simple syrup by combining equal amounts of sugar and water in a medium saucepan. Bring to a boil and simmer until sugar has dissolved. Cool completely before continuing.
Simple syrup can be stored in the refrigerator for up to a month.
Run a slice of lemon around the rim of a champagne flute. Dip in cinnamon sugar mixture to coat rim of glass.
In a blender, combine pumpkin butter, 1 oz. simple syrup, and lemon juice. Blend until smooth. Transfer to a mixing glass or an empty jar. Add ice and gin and shake well. Strain into champagne flute and top with sparkling wine.
