Need advice on the best icing to use on cut-out cake. I am making cut-out letters for Texas A & M (Large T with smaller A & M) about 3 inches thick. The T is 12 inches tall and the top of the T is 10 inches across. The others are 4 1/2 inches both directions. The thing I am most worried about is getting it smoothe inside the small cutout on the A. Don't want to use fondant. Thanks in advance for help.

Or instead of cutting out the small triangle, you can use a contrasting color in buttercream. Black or white.

Just use a crusting buttercream, there are many in the recipe section. Let it set up a bit, 10 minutes, and use a viva paper towel to smooth inside the a, think that would work, you couldn't use a fondant smoother, something smaller that would fit inside the A, maybe a dowel, not sure how small the area would be, i'm sure you could find something.