Prepare the ramekins. Preheat an oven to 325°F (165°C) with a rack placed in the center, then place 6 ramekins inside a large baking dish with deep sides.
Steep the cream. Add 2 cups (475ml) heavy cream and 1 cup (240ml) whole milk to a medium saucepan. Place over medium heat, then bring to a simmer. You’ll know it’s ready when tiny bubbles begin to appear along the sides.
Add espresso. Add 1 cup (200g) sugar, ¼ cup (30g) instant espresso powder, and ¼ tsp kosher salt. Cook, stirring occasionally, until the sugar and espresso dissolve and the mixture is smooth, about 2-3 minutes.
Heat water. Fill a kettle with water, then heat until boiling so it’s ready when needed.
Whisk the eggs. Whisk 6 egg yolks in a large mixing bowl with 1½ tsp vanilla bean paste (or extract) until pale yellow in color, about 2-3 minutes. Temper the eggs by slowly whisking in about ½ cup of the cream mixture, whisking constantly and being careful not to scramble the eggs. Once tempered, whisk in the remaining cream until well mixed. Strain the mixture through a fine mesh sieve before proceeding. I recommend straining it over a large mixing bowl or extra large measuring cup with a spout for easy pouring. Skim off any foam.
Prepare the pots de crème. Divide the mixture evenly between the 6 ramekins. Each should be filled about ¾ way to the top. Pour enough hot water around the prepared ramekins so that it comes about halfway up the sides, then cover the baking dish tightly with aluminum foil. Transfer to an oven and bake for 45-55 minutes or until the custard has set, but is still a little jiggly in the center. They’ll continue to solidify as they cool.
Cool and refrigerate. Let them rest in the water bath for 10 minutes, then carefully transfer to a wire rack. Cool for about 1 hour, then transfer to a refrigerator. Chill for at least 4 hours (but overnight is fine). I cover them individually with plastic wrap.
Serve. When ready to enjoy, allow them to sit out at room temperature for about 10 minutes. Serve each pot de crème with homemade whipped cream or crème fraîche, a pinch of flaky sea salt, and/or chocolate shavings if you like!