In a medium saucepan, combine the heavy cream with the vanilla bean and seeds and the tea leaves and bring to a simmer over moderate heat. In a medium bowl, whisk the granulated sugar with the egg yolks until combined. Slowly whisk one-third of the warm cream into the egg yolks, then whisk that mixture back into the remaining warm cream in the saucepan.
Cook the sauce over moderate heat, stirring gently with a wooden spoon or heatproof rubber spatula, until thickened, 2 to 3 minutes. Set a fine strainer over a medium bowl set in an ice water bath. Strain the sauce into the bowl and let the custard sauce cool, stirring occasionally.
In a large bowl, using an electric mixer, beat the egg whites with the cream of tartar until foamy. Gradually beat in the superfine sugar at high speed until the whites are glossy and hold soft peaks. Beat in the vanilla extract.
Fill a large, deep skillet with 1 1/2 inches of water and bring to a simmer. Using a large spoon, dollop 4 mounds of the meringue into the simmering water and cook over moderate heat until just set on the bottom, about 2 minutes. Gently flip the meringues and cook for 2 minutes longer; do not let the water boil.
Pour the custard sauce into 4 shallow bowls. Using a slotted spoon, transfer the meringues to the bowls, garnish with mint leaves and serve right away.