Great queen backing formula (6)
I believe the answer is:
recipe
'formula' is the definition.
('recipe' can be a synonym of 'formula')
'great queen backing' is the wordplay.
'great' becomes 'epic'.
'queen' becomes 'er' (abbreviation for Elizabeth Regina).
'backing' shows that the letters should be reversed in order.
'epic'+'er'='epicer'
'epicer' reversed gives 'RECIPE'.
(Other definitions for recipe that I've seen before include "Directions for making something" , "method for achieving success" , "Directions for cooking a dish" , "Directions for cooking the turkey e.g." , "Directions for food preparation" .)