Flourish a cereal bowl (8)
I believe the answer is:
brandish
'flourish' is the definition.
(I know that flourish can be written as brandish)
'a cereal bowl' is the wordplay.
'a cereal' becomes 'bran' (type of cereal).
'bowl' becomes 'dish' (a bowl is a type of dish).
'bran'+'dish'='BRANDISH'
(Other definitions for brandish that I've seen before include "Wave something about threateningly" , "shake" , "Wave vigorously" , "Flourish (a weapon)" , "Wave like a weapon" .)