Step 1

Break up 1 pound Chinese slab brown sugar into rough 2-inch pieces with your hands and place in a medium saucepan, or use 2 cups packed dark brown sugar. Add 1 1/2 cups water and bring to a simmer over medium heat (do not let it come to a boil), stirring until the sugar is completely dissolved.

Step 2

Remove the saucepan from the heat. Add 1/2 cup coconut milk, 2 tablespoons vegetable oil, 1 teaspoon vanilla extract if desired, and 1/2 teaspoon kosher salt, and whisk until combined. Let sit for 10 minutes to cool slightly. Meanwhile, place 1 pound sweet rice flour in a large bowl. Coat an 8- or 9-inch round or square cake pan or baking dish with vegetable oil. Prepare a steamer that will fit the pan for steaming.

Step 3

Bring the water in the steamer to a boil over medium-high heat. Meanwhile, while whisking constantly, slowly add the sugar mixture to the flour mixture in 3 increments. Continue to whisk until the mixture is smooth, it will take a few minutes to fully combine. Very small lumps the size of sesame seeds are OK, but if there are larger lumps, strain through a fine-mesh strainer to remove them. Pour into the cake pan or baking dish.

Step 4

Place the pan in the steamer. Reduce the heat to medium, cover, and steam until firm and the center is set when pressed (the top will still be a little sticky), about 1 hour total. Check halfway through and add more water to the steamer if needed. Meanwhile, if using Chinese red dates, halve 4 lengthwise and pit if needed.

Step 5

Place the pan on a wire rack. Sprinkle with 3/4 teaspoon toasted white sesame seeds. Place the dates cut-side down on the cake if desired. Let cool completely, at least 2 hours or up to overnight (cover the pan once the nian gao is mostly cooled if cooling overnight).

Step 6

Run a thin knife around the nian gao to loosen. Slide the knife under the nian gao to lift it up slightly. Slide your hand under the slab and remove it from the pan to a cutting board right-side up. Cut in half, then cut crosswise into 1/4 to 1/3-inch thick slices. It can be served as is or pan-fried.

Step 7

To pan-fry (optional): Heat a thin film of vegetable oil in a nonstick frying pan over medium heat until shimmering. Add a single layer of nian gao slices but do not let them touch. Pan-fry until browned and crisp, 3 to 4 minutes per side. (If desired, dip each slice in beaten egg to completely coat before adding to the pan.)