In a hot, dry fry pan, toast the cardamom seeds, bay leaves, peppercorns, star anise and tea, stirring constantly so they don't burn, until fragrant, 2 to 3 minutes. Using a spice grinder or a mortar and pestle, grind to a fine powder.

In a large bowl, stir together the plums, sugar, lemon juice and spice mixture.
 
Transfer the plum mixture to a large saucepan, set over high heat and bring to a boil, stirring to dissolve the sugar. Once the sugar has dissolved, remove from the heat and let cool. Transfer the plum mixture to an airtight container and refrigerate overnight (this allows the chai essence to develop).

Drain the plum mixture through a fine-mesh sieve. Transfer the syrup to a large saucepan, set over high heat and bring to a boil, stirring until the syrup is reduced by half. Set aside.

In another large saucepan, combine the plums and the vinegar, set over high heat and boil until thickened. Stir in the reserved syrup. Pour the hot jam into sterilized jars and seal. Refrigerate after opening. 

Bloom the gelatin in cold water.

In a saucepan over medium-high heat, combine the cream, sugar and vanilla bean seeds and bring to a simmer, stirring to dissolve the sugar. Remove from the heat. Squeeze out the gelatin and add it to the cream mixture. Cool in an ice bath to room temperature.

Stir the buttermilk and salt into the cream mixture, then strain through a fine-mesh sieve. Pour into serving bowls and refrigerate until set.

When ready to serve, top the panna cotta with the chai-spiced plum preserves and hazelnuts. Enjoy with a glass of Russian River Vineyards Pinot Noir!