Scrub and peel the Russet potatoes, cut them into even chunks and place in large pot. Fill with enough water to cover the potatoes, add a pinch of salt and bring to a boil.
Cook the potatoes for 10-15 minutes, until fork tender.
Drain water, add milk and start mashing the potatoes. Add in butter, cheeses, spices and some salt and pepper. You want these to be stiffer than normal mashed potatoes.
Let the mashed potatoes cool off completely, then refrigerate until ready to fry. They will be easier to handle cold.
Place flour in one bowl, the eggs (beaten) in another bowl and the breadcrumbs in another bowl. Grab a ping pong ball sized amount of mashed potatoes and shape into a small log.
Dip the croquette first in the flour, shaking off excess, then into the egg, then the breadcrumbs. Repeat until all the mashed potatoes are used up.
When ready to fry, grab a medium sized deep pot, pour in 2-3 inches of vegetable oil. Heat on medium-high until the oil shimmers and is hot. Add in 3-4 croquettes at a time.
As the croquettes finish cooking, remove them from the oil with a slotted spoon onto a paper towel. Serve immediately.