Marinate the Beef: In a bowl, toss the sliced beef with 1 tablespoon of the soy sauce and half the dark soy sauce. Set aside for 10 minutes. You'll notice the beef darken slightly as it absorbs the salty liquid.

Prepare the Sauce: In a small bowl, combine the remaining soy sauce, the rest of the dark soy sauce, fish sauce, sugar, and lime juice. Stir until the sugar dissolves; the mixture should smell pungent, sweet, and salty all at once.

Heat the Pan: Place a large frying pan or wok over a high heat until it's smoking hot. Add the oil; it should shimmer and ripple immediately. The sound of the oil hitting the hot metal is your cue that you're ready.

Stir-Fry the Aromatics: Add the chopped garlic and sliced chillies to the pan. Stir-fry for just 15-20 seconds until fragrant. You'll smell the garlic mellowing and the chilli's sharpness blooming — don't let them burn, as they turn bitter.

Cook the Beef: Add the marinated beef in a single layer. Let it sear untouched for 30 seconds to get a good colour. Then, toss vigorously for 1-2 minutes until the beef is browned on all sides but still pink inside. The sizzling sound should be loud and lively.

Add the Sauce: Pour the prepared sauce over the beef. Toss to coat everything evenly. The sauce will bubble up immediately and begin to thicken, clinging to the meat. You'll see a glossy sheen develop on the beef.

Finish with Basil: Turn off the heat. Add the holy basil leaves and toss through for 20-30 seconds. The residual heat will wilt the leaves, releasing a heady, almost peppery fragrance that fills the kitchen. The leaves should be soft but not completely collapsed.

Rest and Serve: Let the stir-fry rest in the pan for 1 minute. This allows the flavours to settle and the sauce to cling perfectly. Serve immediately over steamed jasmine rice, garnished with sliced spring onion.