Clue: Something in the fryer, I appreciate that meal served up into which last of ketchup goes (4,3)
Answer: DEEP FAT
Explanation: Definition: Something in the fryer
An envelope ('into which … goes') of P ('last of ketchu**P**') in DEEFAT, a reversal ('served up' in a down light) of TA ('I appreciate that') plus FEED ('meal').