Rich meal makes rat so happy (5)

I believe the answer is:

roast

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'rich meal' is the definition.
'roast' can be an answer for 'meal' (I've seen this before). I am not sure about the 'rich' bit.

'rat so happy' is the wordplay.
'happy' indicates anagramming the letters (happy can mean slightly drunk).
'rat'+'so'='ratso'
'ratso' anagrammed gives 'ROAST'.

'makes' is the link.

Can you help me to learn more?

(Other definitions for roast that I've seen before include "Cooked meat; criticise" , "Oven joint" , "Traditional Sunday lunch" , "Tear to pieces" , "Cook in oven or by exposure to heat" .)

I've seen this clue in The Sun.

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