Step 1

Preheat oven. Heat oven to 350F/175C. Generously brush a 9x13 baking pan with melted coconut oil on the bottom and sides. Set aside.

Step 2

Toast black sesame seeds. (Skip this step if using black sesame powder). Add black sesame seeds to a dry skillet over medium heat. Toss the seeds from time to time or mix with a wooden spoon, until they begin to crackle and smoke, about 3-5 minutes.

Step 3

Grind black sesame seeds. (Skip this step if using black sesame powder). Transfer seeds to a food processor. Pulse until seeds are finely processed into powder, about 1-2 minutes. Be careful here -- there is a fine line between powder and paste. Pulse the seeds until the oil starts to release and the seeds clump together just a bit; the powder will look moist. But exercise caution -- if you pulse too much, you will end up with tahini paste!

Step 4

Whisk batter together. Scrape sesame seed powder into a large bowl. Add sugar, melted coconut oil, and eggs. Whisk well until smooth, about 1-2 minutes.

Step 5

Add evaporated milk and coconut milk. Whisk well, making sure the batter is smooth and lump-free, about 1-2 minutes.

Step 6

Add glutinous sweet rice flour, baking powder, and salt. Whisk well, sure the batter is smooth and lump-free, about 2-3 minutes.

Step 7

Pour into 9x13 pan. Scrape the batter into the well-oiled pan. It will be very loose and runny.

Step 8

Garnish. In a small bowl, combine remaining 1 Tbsp black sesame seeds and 1 Tbsp white sesame seeds. Sprinkle along the edge of the pan. (If you prefer, double the amount of both sesame seeds and sprinkle completely over the entire top, not just on the edges.)

Step 9

Bake. Slide carefully into oven and bake until done, about 50-60 minutes. Checking for doneness will be challenging, as the batter will remain moist and sticky even when fully baked. Instead, check for doneness by looking for brown edges that naturally pull away from the pan. Give the pan a little shake -- the center of the cake should be set with no jiggle.

Step 10

Cool and serve. Transfer to the counter. Cool for 1 hour (at least) at room temperature. Cut with a serrated knife into 24 squares.