Step 1
Place sixteen 4-ounce ramekins on a rimmed baking sheet.
Step 2
Split vanilla bean lengthwise with the tip of a sharp knife. Holding the pod open scrape seeds from each half using the flat side of your knife.
Step 3
Fill a large pot halfway with water and bring to a simmer over medium heat.
Step 4
Combine vanilla pods scraped beans heavy cream and 1 cup sugar in a large bowl that will fit snugly into the pot; whisk thoroughly to mix. Place bowl over simmering water; whisk until cream mixture is just warm and sugar is dissolved about 5 minutes.
Step 5
Remove bowl from heat and strain cream mixture using a fine-mesh strainer. Pour out hot water.
Step 6
Sprinkle gelatin over 1/2 cup water in a small bowl and stir quickly with a large toothpick until granules are separated. Pour gelatin into cream mixture and whisk thoroughly. Let sit until slightly cool about 20 minutes.
Step 7
Whisk buttermilk thoroughly into cream mixture; pour into ramekins. Cover with plastic wrap and chill until set at least 6 hours and preferably overnight.
Step 8
Place blueberries in a large saucepan over medium heat; cook until slightly toasted and starting to release their juices about 5 minutes. Stir in orange juice and 1 cup sugar. Bring to a simmer and cook until mixture is reduced by half about 10 minutes. Remove from heat and let cool until thickened and syrupy about 30 minutes.
Step 9
Run a thin knife around the edges of each ramekin. Invert panna cotta onto serving plates. Serve topped with blueberry topping.