Make the Thai Tea: For the Thai tea, bring 2 cups of water to a boil. Remove from heat and add the Thai tea mix (or black tea). Let it steep for about 5 minutes. Strain the tea into a pitcher and stir in the granulated sugar until dissolved. Chill in the refrigerator.

Add all the ingredients for the beef into a bowl then submerge the beef into the liquid. Cover with a lid.

Make the mayu: Add garlic and canola oil to a pot, then simmer over low heat for 10 minutes, constantly stirring until it turns black.

Transfer into a blender, add sesame oil, then blend for approximately 30 seconds, so the garlic completely disintegrates. (Store in a sealed container in the refrigerator for up to two months.)

Make the broth: Preheat an oiled pot to medium-low heat. Saute the onion, the garlic, and the ginger for 5 minutes, stirring often.

Add the mushrooms, the leeks, the scallions, and the broth into a pot, taking care that the vegetables are covered by about two inches (5 cm) of broth.

Cook over high heat until the water reaches a rolling boil. Lower the heat to a mild simmer, then cover the pot with a lid. Add the beef into the pot.

Cook until it reduces by about half.

Place the eggs into the broth, lower the heat to a simmer, and cook for about 6 minutes. Place the eggs in an ice bath for a few minutes, then peel them.

Add the noodles to the simmering broth and cook according to the instructions on the package.

Portion the broth into bowls, then season it with the mayu sauce according to taste. Add the noodles and top with slices of Chashu beef and chopped scallions. Slice each in half lengthwise, then place two halves per portion. Enjoy with Thai Tea.