Omurice (Japanese Omelette Rice)

Bahan-bahan (2 porsi)

• ¼ onion ((4 oz, 113 g))
• 3 oz boneless, skinless chicken thigh
• 1 Tbsp unsalted butter
• 1 Tbsp green peas ((cooked))
• ½ tsp Diamond Crystal kosher salt ((divided))
• freshly ground black pepper
• 2 servings cooked Japanese short-grain rice ((1¾ cups, 330 g; warm))
• 5 Tbsp ketchup
• 1 tsp Worcestershire sauce
• 4 large eggs (50 g w/o shell) ((divided))
• ½ tsp Diamond Crystal kosher salt ((divided))
• 2 Tbsp unsalted butter ((divided))