Special equipment: a ricer or food mill and a deep-frying thermometer
For the picadillo: Heat the oil in a large saute pan over medium-high heat. Sprinkle the beef with salt and pepper and cook, stirring to break it up into small pieces, until browned and cooked through, about 3 minutes. Remove to a bowl using a slotted spoon and set aside, allowing the fat to remain in the pan. Add the cumin, garlic, onions and bell peppers and cook until soft and fragrant, 7 to 8 minutes. Add the meat back to the pan along with the white wine, and cook until the wine is reduced by half, about 2 minutes. Add the tomato sauce, raisins, olives, capers and bay leaf and continue to cook until all of the flavors have come together and the liquid is mostly absorbed, about 10 minutes. Add additional salt and pepper to taste and set aside to cool. Once cooled, drain off any excess liquid.
For the potatoes: Place the potatoes in a large pan of cold salted water over medium-high heat. Bring the water to a boil, reduce the heat and simmer until tender, 20 to 25 minutes. Drain the potatoes and put them back in the same pan over low heat, shaking the pan to dry the potatoes, about 2 minutes. Pass through a ricer or a food mill (or mash thoroughly with a large fork) and stir in the butter and cream. Season with salt and pepper and set aside to cool.
To assemble the papas rellenas: Roll 2/3 cup of the mashed potatoes into a ball. Create a well with your thumb and fill it with 2 tablespoons of picadillo filling; completely enclose the filling with some of the mashed potatoes, reforming the ball. Set on a large plate. Continue with the rest of the potatoes and picadillo filling.
Place the flour, egg and cracker meal each in a separate shallow bowl. Roll the balls first in the flour, shaking off any excess, then in the egg and then in the cracker meal. Set the balls on a large plate, cover and refrigerate for at least 1 hour or up to overnight.
Pour 3 to 4 inches of vegetable oil into a heavy-bottomed pan or Dutch oven and place over medium-high heat. Heat until a deep-frying thermometer inserted in the oil registers 375 degrees F. Fry the stuffed potatoes in batches, taking care not to overcrowd the pan and turning the balls to brown evenly, until lightly browned, 1 to 2 minutes. (You know you have cooked them too long if the coating starts to crack.) Remove to a paper-towel-lined plate using a slotted spoon. Repeat with the remaining balls, making sure the oil comes back to 375 degrees F between each batch.
Arrange on a platter and serve while still hot.
This makes more than enough picadillo to fill the papas rellenas. The leftovers can be used to make empanadas, served over rice or frozen for your next batch of papas rellenas.