Step 1
Make the infused baijiu: To a 1-quart jar, add the baijiu and tea leaves, seal, and set aside at room temperature until the baijiu takes on a subtle tea flavor, 4–12 hours.
Step 2
Strain the infused baijiu through a fine-mesh sieve set over a large liquid measuring cup (discard the tea leaves), then pour it back into the jar. (If not using immediately, cover and store in a cool, dark place for up to 6 months.)
Step 3
Make the cocktail: To a cocktail shaker filled halfway with ice, add 1½ ounces of the infused baijiu (reserve the remaining for another use), the umeshu, egg white, lime juice, pineapple juice, and simple syrup. Shake until chilled, about 15 seconds, then strain into a coupe or rocks glass. Discard the ice, pour the liquid back into the shaker, and shake again until foamy, about 15 seconds more. Strain back into the glass, garnish with a dehydrated pineapple slice if desired, and serve.