In a small saucepan, melt the butter over medium heat. Once the butter melts completely, reduce the heat slightly and let the butter bubble for another minute. Once you start noticing tiny golden specks at the bottom of the saucepan and reduce the heat slightly again. Stir the butter with a spatula or wooden spoon. Keep a watchful eye because the butter can burn easily at this stage. Continue heating the butter until more golden specks of milk solids form and then turn brown, like the color of milk chocolate. Turn off the heat and pour the browned butter into a bowl immediately. (For reference, it usually takes me about 4 minutes to melt the butter and brown it to the desired color.)

Toast the sesame seeds in a skillet over medium-high heat. In 2 to 3 minutes, you should be able to smell a faint nutty aroma coming from the seeds and see light wisps of smoke coming up the sides of the skillet. Turn off the heat and let the seeds cool for a few minutes.

While the seeds are still warm, very carefully transfer the seeds to the bowl of a food processor, making sure not to spill the seeds everywhere. You can also transfer the seeds to a bowl first if you think you’re going to make a mess.

Add the browned butter, powder sugar, vanilla, extract, and salt (if using). Blend the mixture for about 4 to 5 minutes, stopping and scraping down the sides of the bowl with a spatula frequently. Keep blending the mixture until you get a runny black sesame mixture (see photo below, left). Transfer the filling to a bowl and chill in the refrigerator for a few hours or freeze for about 20 minutes, until the filling turns solid.

Put on a pair of disposable gloves. Then, line a large plate or quarter sheet pan with parchment paper. Scoop out 10 to 11 grams of the black sesame filling (about 2 teaspoons) and roll the filling into a tiny ball. Transfer the ball to the lined plate (or sheet pan), and continue scooping out and rolling the black sesame filling into balls. After shaping about 12 to 13 black sesame balls, you may start to notice that the butter is melting and shaping the filling is getting messier. I like to pop the filling back into the freezer for 10 minutes at this stage to chill the filling again. Once you’ve shaped all of the black sesame filling into balls, freeze them again for at least 30 minutes or overnight (I usually freeze overnight).

Pour the glutinous rice flour into a medium to large mixing bowl. Then, dip a 1/4 cup metal measuring cup in the saucepan and use it to measure out 3/4 cup of boiling hot water, pouring that hot water over the flour. Be careful during this step or else you may accidentally scald yourself. When you pour the hot water over the flour, you can notice the flour starting to gelatinize (see photo below, left). That’s exactly what we want at this stage.

Use chopsticks or a large fork to stir the water into the flour. Once incorporated, you can cover the bowl with a large plate, silicone lid, or a damp towel and let the dough cool for a minute before kneading by hand. I am okay mixing the dough right away, but I may have slightly more weathered hands that can tolerate heat. Gather and knead the dough together. If the dough is still looking a bit dry (like the photo above, right), pour a tablespoon of the hot water over the loose flour, and continue kneading the dough (I usually need this additional tablespoon of water). Keep kneading the dough until you get a cohesive dough that’s a bit tacky to touch, but not too sticky. Place the dough in the bowl and cover it with a silicone lid, plate, or damp towel. Don’t let this dough sit for too long because it will dry out, making the wrapping process more difficult.

Line a large plate or quart sheet pan with parchment paper. I like to shape the tang yuan 5 at a time. That way, the filling won’t melt as I shape the dumplings, and the dough won’t dry out. Take 5 pieces of black sesame filling out of the freezer and place it on a plate. Then, rip off 5 small pieces of dough that’s between 15 to 16 grams each (just over 2 teaspoons). Leave 1 piece of dough out and place the other 4 small pieces back into the bowl, covered. This dough crusts over and dries out quickly, so try to cover it up as much as possible.

Finally, use your fingers to pinch the opening together to seal the dumpling, making sure that the filling is completely sealed. Roll the ball once again, until you get a smooth, round ball. Transfer the shaped dumpling onto a lined plate or quarter sheet. Continue shaping the remaining 4 small pieces of dough around the 4 black sesame balls. Then, shape the remaining dumplings, 5 at a time.

Once you’ve shaped all the dumplings, you can freeze them for later or cook them now.

Transfer the dumplings to bowls, with a bit of broth. Then, cook the remaining dumplings. Cooked tang yuan are best served immediately to ensure that the filling is still runny and the doughy exterior is nice and soft.