Put the deboned chicken in the "Closed lid" and chop 3 seconds/speed 5. Remove and set aside for use in Step 7. Rinse "Closed lid" .Put onion in "Closed lid" (and garlic if desired) and chop for 2 seconds/speed 5. Scrape down bowl.Put butter and oil in bowl and cook 6 minutes/varoma/speed 1Add flour and cook 5 minutes/110°C/ speed 2Add milk, stock cube(s) (or stock paste or salt), nutmeg, black pepper and some parsely and mix 10 seconds/speed 6Cook 6 minutes/120°C/speed 3Add chopped chook and fold in: 20 seconds/speed 4. Speed 4 seems to be necessary because the bechamel is now very thick.Transfer the mixture to a large flat backing tray and spread to about 1.5cm thick and leave to cool. Once cool, cover with plastic wrap and refrigerate for several (6-7) hours until chilled. This will make forming the croquettes easier because you can turn the mixture out and cut into oblongs.On a flat work surface dusted with flour, form croquettes into 2- to 2 1/2-inch (5- to 6.25-cm) long cylinders about 1 inch (2.5 cm) in diameter. Lightly roll in flour.Place flour in a bowl. Break the egg in a 2nd bowl and thoroughly whisk. Place the breadcrumbs in a 3rd bowl.Dip the croquettes in flour, then the egg (completely covering) and roll in breadcrumbs to completely cover.In a skillet or sauté pan, heat at least 3/4 inch/2 cm of sunflower oil over medium-high heat. Reduce the heat to medium-low.Working in small batches that don’t crowd the pan, fry the croquettes, turning frequently, until they are golden on the outside and hot and creamy at the center, about 2 minutes. Gently transfer them to absorbent paper towels to drain off excess oil. Serve hot or at room temperature (as is the custom in Spain).