Make the Béchamel and polenta far enough ahead of time to chill thoroughly. You'll also need to have a ham hock that's been simmered for about 4 hours or until tender.
For the Béchamel, melt the butter in a small saucepan and fry the leeks until tender but not brown. Add the flour and cook, stirring to saturate with butter, about 1 minute. Whisk in the milk or half and half, continuing to whisk until there are no lumps of flour and the sauce is the consistency of thick gravy. Add the chopped ham hock, salt, pimentón, and white pepper to taste. Cool to room temperature then refrigerate until cold. 2 tablespoons cultured unsalted butter, ½ cups leek, 2 tablespoons flour, ¾ cups milk, ½ cups ham hock, ½ teaspoon kosher salt, white pepper
For the polenta, put all the ingredients in a saucepan and cook, stirring continuously for 20-30 minutes or until the polenta is tender and very viscous. Cool to room temperature, then refrigerate until cold.
2 cups milk, ¾ cups polenta, 1 teaspoon evaporated cane sugar, ¼ teaspoon onion, ½ teaspoon salt, white pepper
To make the croquttes, rub some oil on your hands. Cup one hand and spoon some polenta into it, smoothing out to make a "bowl". Spoon a small amount of Béchamel into the polenta, then cover with another layer of polenta. Seal the edges and form into a puck shape with your hands. Lay on an oiled surface, repeating until you're out of polenta. Refrigerate until firm.
Heat a cast iron pan with about ¾" of oil to 375 degrees F. Prepare 3 bowls, one with flour, one with a beaten egg and the last with panko. Dredge each croquette in flour, dip in the egg, then thoroughly coat in panko, using one hand for the egg and the other for the panko. Fry the croquette until the sides turn light brown, flip, then fry the other side until the whole thing is golden brown. Drain on a paper towel lined wire rack and serve with a dusting of pimentón and tomato jam.
flour, 1 egg, ¾ cups panko breadcrumbs
