“Occassional” spelling problems

I can never remember whether “occasional” has two C’s and two S’s, two C’s and one S, or just one of each. I look up the word every time, and no matter how many times I tell myself that the word has 2 C’s and 1 S, it never sticks and I always have to look it up again. It’s gotten so bad that I’ve occasionally avoided using the word. Intermittently, anyway.