½ cup finely chopped smoked bacon
1 small yellow onion, finely chopped (about ¾ cup)
1 medium apple, finely chopped (such as Macintosh)
¾ cup plus 2 tablespoons all-purpose flour
9 tablespoons unsalted butter
3 cups whole milk
Salt and freshly ground black pepper
¼ cup mayonnaise
1 teaspoon smoked sweet pimentón
2 teaspoons fresh lemon juice
3 large eggs
1 cup all-purpose flour
1 cup panko
1. In a medium skillet set over medium heat, combine the bacon and onion and cook until the onions are translucent and soft, about 7 minutes. Add the apple and cook until it begins to release water, about 4 minutes. Stir in the butter and mix until melted. Add the flour and cook for 2 minutes, whisking constantly. Add the milk little by little, adding more as it is absorbed, until all the milk is incorporated. Cook, whisking constantly, until the taste of flour is gone, 4 minutes. Remove the mixture from the pan and place in a medium bowl. Cover with plastic wrap and place in the refrigerator and chill.
2. Make the aioli: In a medium bowl, combine the mayonnaise, pimentón and lemon juice. Season with salt and set aside.
3. Finish the croquetas: In a medium bowl, whisk the eggs. In another medium bowl, add the flour. In a third medium bowl, add the panko. Remove the mixture from the refrigerator and, using your hands, form ½-inch-round balls. Dip each ball into the flour, then the eggs and finally the panko.
4. In a large saucepot, add enough canola oil to come 4 inches up the side of the pan. Set over medium-high heat and bring the oil to 350°. Add the breaded balls in batches and fry until golden brown, about 1½ minutes. Use a slotted spoon to carefully transfer the croquetas to a paper-towel-lined sheet pan; repeat until all the croquetas are fried. Serve hot with the aioli.