The phrase you might be thinking of is "kill the fatted calf". This is an idiom taken from the biblical parable of the prodigal son.
Here's what it means:
* To celebrate someone's return or a special occasion with a grand feast.
The parable tells the story of a son who leaves home and squanders his inheritance. When he returns, his father welcomes him back with open arms and throws a lavish feast, killing the fatted calf (a prized animal) to mark the occasion.
The idiom "kill the fatted calf" is used to describe a joyful celebration or welcoming of someone special.