First make the mashed potatoes. Peel the potatoes and cut into chunks. Add them to a large pot, cover with water and bring them to a boil. Cook until you can slide a fork into a potato easily. Drain and either rice your potatoes back into the pot or add them back in and mash them well with a masher. Add the butter, cream and salt and mix well. Set aide to cool.
Next make the filling. Add all the filling ingredients to a medium bowl and stir to combine. Set aside.
Make the sauce. Add all the ingredients into a small bowl, stir well and set aside.
Get out three plates or shallow bowls. In one add the panko and season it if necessary. In another, add the egg and beat it with a fork. In the third, place the flour and salt. Arrange them so they go in a line in this order: flour, egg, panko.
Make the balls. First take a tablespoon of the filling and roll it into a ball. Next take 1/8 of a cup of mashed potatoes and roll into a ball as well. Using your thumb, make a hole in the mashed potato ball and slide the filling ball into the hole. Push the mashed potato around the filling ball until its completely covered. If any spots of filling are showing, just take a little potato and patch the hole. Roll the ball around again so its got a nice circular shape. Repeat with the rest of the potato and filling.
Pour vegetable oil into a medium skillet to measure 4 inches deep (you want it to just cover the croquettes) and heat over medium-high until a pinch of breadcrumbs bubbles immediately when added.
Dip potato balls in the flour, then the egg, and then roll in breadcrumbs. Working in batches, fry the croquettes, turning often, until golden brown and crisp, 3–4 minutes. Remove from the hot oil with a slotted spoon. Drain on paper towels.
Serve right away with the sauce!
Nutrition information is for 1/6 of the recipe and without sauce.