Soak the rice noodles in cold water for about 30 to 50 minutes until they soften.

In a wok or large frying pan, heat the butter over medium heat.

Add the diced chicken and sauté until browned. Remove chicken and set aside.

Heat oil in the wok over medium-high heat. Crack the eggs into the hot oil and cook until firm.

Stir in the browned chicken and cook for 5 minutes.

Add the softened noodles, sugar, fish sauce, vinegar, and red pepper flakes. Stir-fry everything until the noodles are tender. Adjust seasonings to taste.

Stir in the bean sprouts and cook for an additional 3 minutes.

Serve the Pad Thai hot, garnished with chopped green onions, crushed roasted peanuts, and a wedge of lemon.