Hello! I need some help or reassurance:
I have my second wedding cake due Friday.
Today, I started making the white chocolate buttercream frosting that will fill the layers (four layers in each of the four tiers)and go under the fondant.
I have never tried this white chocolate buttercream recipe before, and now I am suspecting it may be too light and poof out between the layers under the weight of the cake after I've covered it, thus making my fondant-covered tiers appear lumpy. I've added more confectioner's sugar to give it more structure, but now I'm just freaked out. Can someone help put my mind at ease here or give me a tip to keep this from happening? The poofing out, I mean? The freaking-out I'm sure just comes with the territory.
I reeeeeally appreciate your help or advice. Thank you in advance!

You can make a damn out of the buttercream - you have to make the buttercream very thick by adding more powder sugar. You pipe a damn around the perimeter of the cake and add your filling. It should hold in your filling when you put another layer on top of it. I hope this helps.

I make white chocolate buttercream by combining white chocolate ganache with some buttercream it has a pretty good consistency.

When I use buttercream, all I use is white chocolate buttercream. It is VERY soft after you first make it. I let it set for about 30 minutes before I starte filling & icing my cakes. Once they are crumb coated, the set up very nicely. I then put a light layer on top of it then add my fondant, works like a charm. The recipe I use for my white chocolate butter cream is:
1 16 oz back white chocolate chips (I use Hershey - not too sweet)
1/2 cup heavy cream
2 cups (4 sticks) unsalted butter, softened
4 cups (1 2lb bag) powdered sugar.
Put chocolate chips & cream in microwave for about 1 1/2 minutes, or until melted.
Pour chocolate mixture into stand mixer, add 1 stick butter on med-high speed til mixed, then 1/4 sugar at lower speed and repeat until all are incorporated.

What is in your recipe besides white chocolate? It is hard to say without knowing all the ingredients.

Thanks SO much folks!

@LindaF144, per batch, I am using about 8oz Callebaut white chocolate (melted and cooled until thick-does that qualify as ganache-like?) 1.5 cups room temp unsalted butter, 4 cups confectioner's sugar, about a 1/2 teaspoon of vanilla, and a splash of heavy cream.

@msulli10, yes, thanks, I use a dam of about a quarter inch (a #12 tip). Should it be smaller do you think?

@MHCakes2, thank you for sharing your recipe! I wonder why it helps to let it set? Do you know?

I think the reason for letting it set, is the chocolate and butter both start setting back up, so it starts firming up.