I dont know what I did wrong, but I think it may have been in the doubling of the recipe (it said it was enough for 12, i was making 24 cupcakes).

More specifically I suspect the problem was the butter. When i tried to make this in my stand mixer, I thought it was going ok until i decided to unhinge the bowl from the machine. when i tried to scoop it out into a pastry bag to practice icing, I was greeted with a deep spoonful of liquid!! I tried draining it, and it just kept coming. I was very surprised at how much liquid was hidden at the bottom of the bowl.

I managed to somewhat save the icing with emergency store bought lemon icing to mix it with, but Im not proud of that. :/
Anyways, here it is unaltered. Double it , and you'll have the amounts i used.

Here it is, unaltered:
2oz pureed strawberry
1/2 sugar
2 large egg white
6 oz butter
1/2 tsp extract

I'm hoping that the recipe followed meringue buttercream instructions; ie heating the 1/2 sugar with the egg whites and whipping until 165 degrees then whipping until cool and glossy. then adding in the butter until it comes together, then the strawberry puree.

From what it seems, the proportions of this recipe seem okay. But meringue buttercreams can be a bit tricky if the eggs aren't cooked enough or the mixtures isn't allowed to become emulsified.

Successful Swiss or Italian meringue buttercream is more a matter of careful technique than anything else. I find that having the butter at room temperature helps insure success every time. I also whip the meringue a loooong time so that it doesnt curdle. Only after it is cooled, well mixed and glossy do I add fruit additives like pureed strawberries. I highly recommend Rose Levy's book Cake Bible for all the little details of Swiss, Italian or Mousseline frostings Good luck

Well, I am in the process of trying this again, and in my attempt to get it to 165 i somewhat overcooked it, it now tastes a little eggy. The highest i could get it was 145. :/