Preheat oven to 350°F/175°C.
Make Caramel: Add sugar to a small saucepan and cook the sugar over medium high heat until the color turns golden. Then, remove from the heat and immediately pour the hot caramel into the bottoms of the 4-inch round pan, quickly and carefully tilt the pan to coat the bottom evenly. You should wear gloves at this step as the caramel will be so hot. Set aside to let the caramel harden.
Make Custard: In a medium saucepan, whisk the heavy cream, milk, condensed milk and matcha powder until combined. Bring the mixture to simmer over medium heat, until it starts to bubble just around the edges. Do not bring it to boil. Stir occasionally, the mixture turns light green as matcha powder is incorporated into the liquid. Remove from heat and set aside.
In a medium mixing bowl, whisk eggs, salt and vanilla extract until combined. Slowly add the hot milk mixture to the eggs mixture while whisking the egg mixture constantly to prevent curdling. At this step, make sure to whisk constantly but lightly to avoid creating bubbles in the mixture. Strain the mixture into a large bowl to remove bits of curdled eggs then transfer strained custard into the prepared round pan with caramel at the bottom.
Place the round pan in the center of a baking or roasting pan to make a water bath. Pour in boiling water until it reaches halfway up the sides of the round pan. Bake for 30-35 minutes until custard has set at the edges but still slightly jiggly in the center when you gently shake. The custard should not be completely set when it is removed from the oven; it will continue to cook as it cools. Remove the pan from oven and allow it to cool to room temperature, then chill in the refrigerator for at least 2 hours, preferably overnight.
Once it's cooled, run a sharp knife around the edges of the pan. Flip a large serving platter over the round pan, and quickly invert the custard on the platter. Enjoy!