In a medium saucepan over medium-low heat, combine the heavy cream, vanilla, and crushed ginger. Cook until the edges start to bubble. Remove from heat and let everything steep for 15 minutes.
In a medium bowl, whisk together the egg yolks and 6 tablespoons of sugar until well combined.
Temper the egg yolk mixture by pouring a small amount of the warmed cream mixture into the yolks and whisking to combine until done. Strain the mixture through a fine-mesh sieve into a large liquid measuring cup with a pour spout.
Divide the custard evenly into six 6-oz ramekins. Release any air bubbles on the surface by gently tapping with a spoon. Cover each ramekin tightly with aluminum foil.
Place 1 1/2 cups water in an Instant Pot. Set a trivet or sling inside the pot. Nestle the ramekins on the trivet. Mine can fit 3 of the 6-oz ramekins.
Lock on the lid and make sure the pressure valve is set to seal. Use the manual function to set to cook for 5 minutes on LOW pressure.
When the cook time is up, let the pressure naturally release for 10 minutes. Manually release any remaining pressure and carefully remove the lid.
Carefully transfer the ramekins from the Instant Pot to a wire rack to cool slightly, about 20 minutes.
Add 1/2 cup of water in the Instant Pot before you cook the second batch.
Place the remaining ramekins in the Instant Pot and repeat the steps above.
Chill the ramekins uncovered in the refrigerator for at least 4 hours, or overnight.
To make the roasted rhubarb, preheat the oven to 350 degrees F.
Place chopped rhubarb and vanilla extract in baking dish. Scatter sugar over rhubarb.
Roast rhubarb, tossing once, until tender and juices are syrupy, about 15 minutes. Let it cool to room temperature.
When ready to serve, sprinkle 1/2 tablespoon of sugar evenly on top of each creme brulee. Using a kitchen torch, brulee the tops until the sugar begins to bubble and turn dark golden brown. Let the creme brulee sit for about 5 minutes.
Top the cooled creme brulees with roasted rhubarb and serve immediately.