To make the filling, melt the butter in a saucepan over a medium heat. Add 115g of flour and cook for a minute or so. Gradually add the milk and cream, whisking well all the time to ensure there are no lumps. Increase the heat slightly and bring the sauce to the boil. Turn the heat down and cook the sauce gently for 5 minutes, stirring often, by which time it should have thickened. Stir in the prawns and season with 1 teaspoon of salt and plenty of black pepper. Spread this mixture out on a lined baking tray, cover the surface with a sheet of baking paper and leave to cool. Place the mixture in the fridge for 2 hours to firm up. Preheat the Retigo combi oven on hot air 0% to 230C. Put rest of the flour, eggs and breadcrumbs in three separate wide bowls. Using two dessertspoons, scoop out eight portions of the prawn mixture, each weighing about 20g, and drop them into the flour. Mould them with your hands into rough cork shapes and dip each into the beaten egg. Finally, coat each thoroughly in the breadcrumbs. Repeat with the rest of the mixture. Spray the Retigo bake GN container with thin layer of oil using Retigo oil gun, place the croquetas on it and spray them with oil over the top. Fry in Retigo combi oven for about 4 minutes. Drain on kitchen paper. Serve immediately.