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1
Mix beef with 1 teaspoons sugar, the salt, pepper, and 1 tablespoons oil in a bowl.
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2
Let marinate at room temperature 2 hours.
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3
Whisk together remaining 1 tablespoons sugar, the vinegar, mirin, soy sauces, and fish sauce until sugar has dissolved.
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4
Divide meat into 2 equal portions.
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5
Heat a large wok or a large frying pan over high heat until very hot but not smoking.
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6
(Non-stick pans should not be used.
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7
).
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8
Add 3 tablespoons oil to wok and heat until shimmering but not smoking.
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9
Add half the beef in a single layer and sear until a brown crust forms underneath, about 30 seconds.
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10
Flip cubes and cook 30 seconds on second side.
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11
Add half each of red and green onions and cook, stirring, about 30 seconds.
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12
Add half the soy sauce mixture and shake wok to coat beef.
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13
Add half each of garlic and butter and shake wok to distribute evenly.
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14
Transfer to a bowl and keep warm.
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15
Wipe wok clean and return to high heat.
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16
Repeat steps 4 and 5 with remaining 3 tablespoons oil, beef, red and green onions, sauce mixture, garlic, and butter.
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17
Arrange chopped lettuce and tomatoes on a platter; top with beef and vegetables.
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18
Prepare Dipping Sauce by grinding chiles in a mortar with 1 teaspoons salt to a paste using a pestle.
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19
Transfer to a small bowl and stir in remaining 1 teaspoons salt, the pepper, and lime juice.
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20
Serve the dipping sauce on the side to dip the beef and lettuce bites into.
