Son wants for his birthday but I don't want eggs in it bc of allergy issue.
Not exactly a tiramisu recipe, but a solution.
In many tiramisu reicpes (like the one linked below) the eggs are mixed with sugar and milk to make a custard, which is later mixed with the mascarpone.
If you find a vegan custard recipe you like, substitute that for the custard part of a standard tiramisu and you have your dessert.
You specifically asked about the filling.
But I just remembered (you probably know) the ladyfingers used in tiramisu are also made with eggs.
So you'll have to find a substitute cookie, or a ladyfinger recipe without eggs, to make this safe for your son.
Gordon Ramsay has apparently published a recipe but the UK website that hosted it is apparently defunct.
He just substitutes whipped heavy/double cream at a ratio of about 1/4 cup of cream per egg yolk. Whip the heavy cream until it just forms soft peaks, then fold into the mascarpone and sugar + flavorings until just combined. Should do the trick.
I use this recipe: https://food52.com/recipes... all the time, and it's great! The flavors are actually cleaner and stronger than the traditional egg-based recipes. I add more booze, though!