Preheat the oven to 350°F. Line two baking sheets with parchment.
In a large bowl, beat together the cake mix, eggs, oil, water, and chai spice until smooth and thick.
Scoop 2-tablespoon mounds of batter onto the prepared sheets, spacing 2 inches apart. Bake 10–12 minutes, until set. Cool completely.
Beat the cream cheese and butter until fluffy. Beat in the powdered sugar one cup at a time, then the vanilla, until smooth.
Spread or pipe the filling onto the flat side of half the cakes; top with the remaining cakes to make sandwiches.