In a large skillet, melt the butter over medium heat. Add the onion and cook until translucent, about 5 minutes. Add ¾ cup of flour and stir to blend well. Cook the mixture, stirring frequently until the flour begins to turn golden and smell toasty about 5 to 7 minutes. Add the milk in a slow steady stream, whisking continuously.

Add the chicken and season to taste with salt, pepper, and nutmeg. Stir to combine and cook until the mixture is warmed through and thickens up slightly more, about 2 minutes. Adjust seasoning if needed. Transfer the pan to a wire rack and let the filling cool to room temperature, about 30 minutes.

I used wire cake cooling racks over my plastic cutting board that is reserved for meat and poultry. Even though the chicken is cooked, there is still a danger of cross-contamination. I used a small ice cream scoop. Take a rounded tablespoon of the cooled filling and roll it in your hands to make a small cylinder. Dredge the cylinder in the remaining ½ cup flour, then in the eggs and then in the breadcrumbs. Repeat with the remaining filling.

Put the breaded croquetas in the refrigerator for about 30 minutes to set. If you do not have a Nesco, then use the oven. Preheat the oven to 200° and place a wire rack on a rimmed baking sheet. In a 4-quart saucepan, add enough olive oil so that you’re able to completely submerge the croquetas. Heat the oil to 375°. Working in batches, fry the croquetas until golden brown, about 1 minute per batch. Drain on paper towels, then season lightly with salt. Transfer to the prepared baking sheet and place in the oven to keep warm until ready to serve.