Step 1: In a small bowl, sprinkle 1.5 teaspoons of powdered gelatin over 2 tablespoons of cold water. Let it sit for 5-10 minutes to bloom.
Step 2: In a medium saucepan, combine 1 cup of heavy cream, 1/2 cup of whole milk, and 1/4 cup of granulated sugar. Heat over medium-low heat, stirring until sugar dissolves and mixture is steaming, but not boiling. Remove from heat.
Step 3: Whisk the bloomed gelatin into the warm cream mixture until completely dissolved.
Step 4: In a small separate bowl, whisk 1 tablespoon of matcha powder with 2 tablespoons of warm milk (taken from the saucepan before gelatin was added) until a smooth, lump-free paste forms.
Step 5: Pour the matcha paste into the cream mixture and whisk thoroughly until the color is uniform.
Step 6: Carefully pour the matcha panna cotta mixture into 6 individual serving glasses or ramekins, filling them about halfway. Refrigerate for 1-2 hours, or until partially set.
Step 7: While the matcha layer chills, prepare the white layer: In another small bowl, sprinkle the remaining 1.5 teaspoons of powdered gelatin over the remaining 2 tablespoons of cold water. Let it bloom for 5-10 minutes.
Step 8: In a separate medium saucepan, combine the remaining 1 cup of heavy cream, 1/2 cup of whole milk, 1/4 cup of granulated sugar, and 1 teaspoon of vanilla extract. Heat over medium-low heat, stirring until sugar dissolves and mixture is steaming. Remove from heat.
Step 9: Whisk the bloomed gelatin into the warm cream mixture until completely dissolved.
Step 10: Let the white panna cotta mixture cool slightly at room temperature for 10-15 minutes to prevent it from melting the partially set matcha layer.
Step 11: Once the matcha layer is partially set and the white mixture has cooled, gently pour the white panna cotta mixture over the matcha layer in each glass or mold.
Step 12: Return the glasses or molds to the refrigerator and chill for at least 4-6 hours, or preferably overnight, until both layers are completely set and firm. Garnish as desired before serving.