When we say potato we mean russet potatoes.
When we say medium sized we mean about 5 inches long like the russet on the top of the board.
We use russets for most of our recipes. Russets are a good all purpose potato. They are relatively inexpensive and are always available. If we are using another kind we will put it in the recipe. They may not be the absolute best for all recipes. But in my world the best potato to use is the one I have. And I most always have russets.
As you can see russets potatoes are kind of the ugly duckling of potatoes. They are brown skinned with uneven coloring, dimples and bumps. They are usually bigger than other potatoes.
I put in a couple of other kinds of potatoes on the board so you could compare sizes. If you are using a smaller potato you are going to need more than stated in our recipes.
In the middle of the board we have three Yukon gold potatoes. They are delicious. I cut one open for you so you could see the flesh is actually yellow, hence “gold”.
The red potatoes on the bottom of the board are even smaller.
You can always use what you have, just adjust for size. None of our recipes are so precise that you can go wrong. It’s all about what is going to fit in the pan for the most part.