1. Toast the sesame seeds in a dry wok or frying pan over a gentle flame for 5-10 minutes, stirring constantly, until they smell and taste delicious. Because they are black, you won’t notice a change in color, so do take care not to burn them—they will taste bitter if overdone. Trust your nose and tongue to tell you when they’re ready—the roasted aroma and taste are unmistakable.
2. When the seeds are done, use a mortar and pestle to grind them coarsely (this can be done in a food processor, but take care not to reduce the seeds to a powder—they taste better with a little crunch). Add the sugar to the crushed seeds and mix well.
3. Heat the lard or coconut oil over a gentle flame until melted, and then stir into the seed mixture. Press the stuffing firmly into a baking sheet making a layer about ¾ inch thick, and refrigerate until set. When you are ready to stuff the tang yuan, use a table knife to cut the stuffing into ¾-inch cubes.
Making the tang yuan:
1. Mix the two flours together. Add the water and stir to make a soft, squishy dough (you can add a little more glutinous rice flour or water if you need to adjust the consistency).
2. Divide the dough into 2 or 3 parts. Working on a surface dusted with rice flour or glutinous rice flour, roll each part into a sausage about 1½ inches thick and break off pieces the size of small walnuts.
3. Take one piece of dough, flatten it slightly and use your thumb to make an indentation in its center. Place a cube of stuffing in this indentation and then draw the sides of the dough up around it to enclose it completely. Roll it gently between your palms to make a round ball. (Make sure there is no stuffing peeking out or the dumpling will disintegrate when you cook it.) Lay the finished tang yuan on a tray or bamboo platter dusted with flour until you are ready to cook them (they can be made in advance and frozen or refrigerated).
Making the dip:
Combine the sesame paste and sugar in a tiny serving bowl, adding enough toasted sesame oil or oil from the sesame paste jar to give a good dipping consistency if you like. (In snack restaurants each helping of 2-4 dumplings is served in a small rice bowl with an accompanying tiny saucer of sesame paste and sugar.)
Cooking the tang yuan:
1. Fill a large pot with water and bring it to a boil. Add the tang yuan, one at a time, and simmer them for about 15 minutes. Do not allow the water to bubble vigorously or it will rupture the dumplings—keep an eye on the pot and throw in half a coffee-cupful of cold water as necessary to calm the water down.
2. Serve the tang yuan in small bowls filled with some of the hot cooking water to keep them warm. Your guests should lift them out of the water with chopsticks and dip them in the sesame paste to eat.
Several tang yuan fillings are used in Sichuan, most based on a simple mixture of white sugar and lard. For rose-flavored stuffing, add to the sugar-lard base a small amount of candied rose petals; for tangerine stuffing, add finely minced candied tangerine and crushed rock sugar; for cherry stuffing use glace cherries; for three-nut stuffing add walnuts, melon seeds, and peanuts that you have roasted and crushed to a coarse meal.
Mr. Lai used to make tang yuan stuffings out of sweet-scented osmanthus blossoms and jujube (Chinese date) paste, and then serve one of each of four different types of tang yuan in the same bowl (this is known as si wei tang yuan, four-flavor tang yuan). Four-flavor tang yuan can be given an extra flourish by molding each type of dumpling into a slightly different shape, so there are egg-shaped and pointed tang yuan as well as the ordinary round ones.