Combine heavy cream, milk and sugar in medium pot over medium-low heat. Whisk to incorporate sugar and bring to a light simmer. Place matcha powder in small bowl. Add hot water in a steady stream and whisk in with bamboo whisk until matcha is fully dissolved and no clumps remain. Add matcha mixture to cream mixture. Add gelatin and bring heat to medium. Whisk mixture continuously for 1 minute to set gelatin. Remove mixture from heat and transfer into ramekins or silicon molds of your choice. Let set minimum 4 hours in refrigerator.
For sesame glaze, combine sesame paste, sugar, and water in small saute pan on low heat. Whisk continuously until sugar dissolves and mixture is well incorporated. Place in suitably sized container and let cool in refrigerator.
Serve panna cotta with sesame glaze and kumquats, if desired.
PRO TIP: If panna cotta are in molds and will be unmolded for serving, place in freezer 10-15 minutes before unmolding for an easier unmolding experience!