I would like to try Anthonia's icing, and I do not have meringue powder. Is there any alternative ingredient that I can use to replace ?

The recipe :

6 oz (3/4 cup) of warm water
5 Tablespoons meringue powder
1 teaspoon cream of tartar
1 kilogram (2.25 lbs.) powdered icing sugar

You can omit the water and the meringue powder for 6 large egg whites.

The brand of meringue powder I use is also flavoured with vanilla, so you may need to add that too.

(Don't use any oil-based flavour extracts though, this icing should be free of any oil/oil residue so that it can harden properly.)

Does anyone know if you can use egg white (powdered form) from the regular grocery store in place of this? If so, do you use more than the Wilton meringue powder?

Thanks antonia