With two curious cats in our house, we've started inverting large mixing bowls over the susceptible ingredients. This works especially well when we're softening butter, warming frozen dough, or whenever we have ingredients out on the counter for more than just a few minutes. (Read: whenever we're likely to have our backs turned for more than a few minutes!)
If your cats figure out that they can nudge the bowl - and what's underneath - off the counter, you could also put ingredients in a cupboard or the microwave until they're needed.
How do you deal with cats on the counter?