Calculus Based Microeconomics Book
If you would like to go step above Varian's intermediate microeconomics and you like Varian as an author then his book Microeconomic Analysis is on graduate level.
However, I personally prefer more  Mas-Colell,  Whinston, and Green (MWG) Microeconomic theory. That is probably the most comprehensive microeconomics textbook there is on the market.