1. Make the filling: Boil potatoes in salted water until fork tender. In a saucepan, melt ½ cup butter with heavy cream. Add boiled potatoes to butter-cream mixture and whip until smooth. Set aside.
2. In a sauté pan, cook onions in remaining butter until translucent. Stir in cooked chorizo, then add whipped potatoes and spices. Stir to combine, salt to taste, and refrigerate until completely cooled, about 2 hours.
3. Make the breading: Meanwhile, combine nutritional yeast, breadcrumbs, and salt in a food processor. Set up a breading and frying station by placing flour in one bowl, beating eggs in bowl, and placing the breading mixture in a third bowl. Fill a saucepan or dutch oven fitted with deep fry thermometer with enough oil to submerge croquettes, about 3 inches. Heat oil to 350 degrees.
4. To form croquettes, scoop 1½ ounces of filling and roll into a ball. (For a classic croquette shape, roll it lengthwise to form a small cylinder, about the size of a wine cork.) A cold mixture is the key to rolling successfully. Begin breading process by dipping croquette into flour, then eggs, then breadcrumbs. Gently place croquette in oil and fry until breading is crispy and browned, 2 to 3 minutes. Remove from oil and drain on a paper towel for at least 5 minutes. Repeat the process with remaining filling.