notre = our (singular noun follows)
leur = their (singular noun follows)
nos = our (plural noun follows)
votre = your (singular noun follows)
Since the noun following the possessive adjective is "pâtisserie préférée" (fém. pl.), we can eliminate nos.
Futhermore, (our) is in brackets, that eliminates leur and votre.
What is left is "notre", which agrees (singular) with the noun following, and also it means "our", as required.