Something in the fryer, I appreciate that meal served up into which last of ketchup goes (4,3)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

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’).