Making Crispy Chilli Beef can be accomplished easily by following these steps:

1. Prepare the Beef: Slice the beef fillet into thin strips. This helps in cooking evenly and becoming tender.
2. Marinate the Beef: In a bowl, combine the sliced beef, soy sauce, baking soda, salt, and black pepper. Let it marinate for about 15 minutes.
3. Coat the Beef: After marination, sprinkle the cornstarch over the beef strips and toss until evenly coated. This ensures a crispy texture during cooking.
4. Heat the Oil: In a deep pan or wok, heat the vegetable oil over medium-high heat. The oil should be hot enough for frying.
5. Fry the Beef: Carefully add the coated beef strips to the hot oil. Fry in batches to avoid overcrowding. Cook for about 3-4 minutes until crispy and golden brown.
6. Drain Excess Oil: Use a slotted spoon to transfer the fried beef onto a plate lined with paper towels to absorb excess oil.
7. Prepare the Sauce: In a separate pan, combine the oyster sauce, sugar, rice vinegar, and minced garlic and ginger. Let it boil on low heat for about 2-3 minutes.
8. Add Chilis: Stir in the sliced red chili peppers into the sauce and mix well.
9. Combine: Add the crispy beef to the sauce, stirring well to coat all pieces evenly.
10. Garnish: Remove from heat and garnish with chopped spring onions and sesame seeds before serving.

Following these straightforward steps, you’ll create a dish that will surely knock everyone’s socks off!