Bring 1 1/4 cups (300 ml) of water to a boil. Pour the water over loose lapsang souchong tea leaves and let steep 30 minutes. Pour tea infused water through a sieve to remove tea leaves. Press the leaves with the back of a spoon to remove as much tea from the leaves as possible. Discard leaves. Let tea cool completely. Use the tea in the following marshmallow recipe. You may have a little tea left over at the end which can be discarded.
Lightly coat an 8×8 inch baking pan with cooking spray and set aside.
Prepare the marshmallow coating: sift together confectioner’s sugar and cornstarch in a large bowl and stir until just blended; set aside.
For the bloom: Whisk together gelatin and 1/3 cup (80 ml) tea in a small bowl and let soften for 10 minutes.
For the sugar syrup: In a medium saucepan over high heat, stir together sugar, 1/4 cup (84 grams) of the corn syrup, 1/4 cup (60 ml) tea, and salt. Boil, stirring occasionally, until the temperature reaches 240°F.
While the sugar syrup cooks, pour the remaining 1/4 cup (84 grams) corn syrup into the bowl of an electric mixer fitted with the whisk attachment. Microwave the gelatin for about 10-15 seconds or until completely melted. Pour the gelatin into the mixing bowl, set to a low speed and keep it running. When the syrup mixture reaches 240 °F, slowly pour it into the mixing bowl with the gelatin mixture. Increase the speed to medium and whisk for 5 minutes, then increase speed to medium high and beat for 3 minutes. The finished marshmallow mixture will be more than doubled in volume. Immediately pour the marshmallow into the prepared pan and sift prepared coating evenly over the top; let stand in a cool, dry place for at least six hours.
Using a knife, loosen the marshmallow from the edges of the pan. Invert the slab onto a work surface dusted with the prepared coating. Cut into about 1 1/2 inch (4 cm) pieces and dust sticky edges with coating. Marshmallow may be stored up to 2 weeks in an airtight container.