Melt the butter in a large saucepan over a medium heat. Whisk in half of the flour to form a smooth paste, then cook the mixture for 30 seconds.
Slowly whisk in the milk, allowing each addition of milk to be absorbed into the mixture and the sauce to thicken, until you have a very thick sauce – almost with the consistency of mashed potato. Season, to taste, with salt and freshly ground black pepper.
Scrape the mixture into a large bowl, then stir in the serrano ham, cooked chicken and parsley. Season again with salt and freshly ground black pepper, then stir in the flaked almonds. Set the mixture aside to cool completely. Chill in the fridge, covered, for at least 10 minutes, or overnight, until it has firmed up.
Take spoonfuls of the chilled mixture and, using wet hands, roll them into balls or cylinder shapes.
Sprinkle the remaining flour onto a plate and season with salt and freshly ground black pepper. Beat the eggs in a bowl. Add the breadcrumbs to another bowl.
Dust each croqueta first in the flour, then dip into the beaten egg, then roll in the breadcrumbs to cover.
Meanwhile, heat the vegetable oil in a deep-fat fryer to 170C, or heat the oil in a deep, heavy-based frying pan until a breadcrumb sizzles and turns brown when dropped into it. (Caution: hot oil can be dangerous. Do not leave unattended.)
Lower the croquetas into the hot oil in batches and fry for 3-4 minutes, or until golden-brown and hot all the way through. Remove from the pan using a slotted spoon and set aside to drain on kitchen paper. Repeat the process with the remaining croquetas.
While the croquetas are frying, heat the olive oil in a separate frying pan over a high heat. Add the padrón peppers and sprinkle with half the salt. Fry for 2-3 minutes, or until just golden-brown on both sides and softened. Transfer to a serving bowl and sprinkle with the remaining salt.
Serve the croquetas with the padrón peppers.