Use only Russet potatoes, which are sometimes called "Idaho" potatoes. Never use red potatoes for mashing, as they mash with a gluey consistency.
Heating the milk before adding it also helps you get the right consistency.
Adding seasonings to the water ensures the potatoes will absorb them. Starches do not absorb flavor as well after they are cooked.
Some sites tell you to steam your potatoes, but I think having the potatoes right in the water with the herbs gives them more flavor.
1. Scrub the potatoes, chop into 2" chunks.
I leave the skins on unless the potatoes have begun sprouting eyes.
2. Cover with water and place on a burner, uncovered.
*Option: You could try cooking them in veggie broth instead for a different flavor.
3. Add a tablespoon of rosemary, about a teaspoon each of salt and garlic powder. You'll have to stir it a few times to keep the herbs from accumulating on the sides of the pan.
*Add as much or as little as you like of any spices you desire. Or just add salt if you're not a spice girl. (See what I did there?)
4. Cook until fork tender. Don't cook them too much. You don't want them mushy. Just fork tender. Then drain the water and pour the potatoes into a big mixing bowl.
5. Mash with a potato masher. Then beat them with a hand mixer.
6. Melt the butter and pour on. Mix some more.
7. Heat the milk in the microwave for about 1 minute. Test with fingertip. You want it hot but not boiling. Pour in the milk and keep mixing.
Add as little or as much milk as it takes to get the consistency you want. But always heat it first. Add the milk a little at a time, so you don't get it too thin.
8. Taste the potatoes. Tasting is crucial. Add more rosemary, garlic, a dash of onion powder, salt, and a bit of pepper a little at a time, mixing and then tasting until they are just the way you want them.
9. Top with fresh chives. I used garlic chives straight from the garden for mine.