If you're going to make those waffles, you'll need some buttermilk!
Buttermilk is one of the simplest dairy products to make. All you need is some milk and a starter culture. For a starter culture, I begin with a small carton of cultured buttermilk from the store; in future batches, you can just use some from your previous batch.
How to Make Cultured Buttermilk
1/3 cup cultured buttermilk (either purchased or saved from a previous batch)
enough milk to fill up your quart jar
Mix together, let stand at room temperature, tightly covered, 1-2 days (until the smell and consistency look right)
Store in refrigerator.
Couldn't be simpler!
If you're adventurous and have access to raw milk, you can try making this without a starter culture; the enzymes and bacteria in raw milk naturally turn milk into buttermilk! Just make sure your milk is clean and fresh when you start.
In case you were wondering, cultured buttermilk is not the same as the buttermilk left over from making butter. You can culture the buttermilk you have leftover from making butter, though, and it works great (that's what I usually do).