Preheat the oven to 350°F (175°C).
In a large bowl, cream together the butter, brown sugar, and white sugar until smooth and fluffy.
¾ Cup butter, 1 Cup brown sugar, ½ Cup white sugar
Mix in the egg until fully incorporated.
1 Lrg egg
Stir in the water and vanilla.
¼ Cup water, 1 tsp vanilla
Add the oats, flour, salt, baking soda, Chinese five-spice, and cornstarch. Mix until a soft cookie dough forms.
3 Cups oatmeal, 1 Cup all-purpose flour, 1 tsp salt, 1 tsp baking soda, 1 tsp Chinese Five Spice
Stir in the black sesame seeds.
2 tsp black sesame seeds
Drop teaspoons of cookie dough onto a baking sheet, leaving space between cookies as they spread.
Bake for 12–15 minutes, until the edges are lightly golden brown.
Allow the cookies to cool on the baking sheet for several minutes before transferring them to a wire rack.