In a skillet over medium heat, melt 2 tablespoons of butter until bubbly. Add 1 diced onion and 2 diced spring onions, stirring occasionally for about 5 minutes until soft and translucent.

In a large mixing bowl, combine the sautéed onions with 1 cup of crab meat, seasoning with salt and black pepper to taste. Stir to combine, ensuring the crab meat is fully incorporated.

In the same skillet, melt 2 tablespoons of butter over medium-low heat. Whisk in 2 tablespoons of all-purpose flour, stirring constantly for about 2 minutes to create a roux. Gradually add 1 cup of whole milk, whisking until thickened, about 4-5 minutes.

Once the béchamel has thickened, remove it from heat and fold it into the crab mixture until well coated. Allow it to cool in the bowl for about 30 minutes.

Once cooled, take small portions of the mixture and form them into patties or ovals about 2 inches wide. Dust each croquette with all-purpose flour.

In a shallow bowl, beat 1 egg and set aside. Dip each floured croquette into the egg, then roll them in panko breadcrumbs until fully coated. Let them sit for about 10 minutes.

In a large frying pan, heat about 1 inch of neutral oil over medium-high heat until it reaches 350°F (175°C). Fry the croquettes in batches for about 3-4 minutes on each side until golden brown and crispy.

Once golden, use a slotted spoon to transfer the croquettes to a plate lined with paper towels. Garnish with parsley if desired.