Step 1

Mix the cookie crumbs with the butter. Scoop out about 2 tablespoons of the crumb mixture into each of four (1-cup) ramekins or custard cups and press it down to make a layer a scant 1/4 inch thick. You may not need all the crumbs, but you can reserve them and sprinkle over the top of the cheesecakes as garnish.To make the filling

Step 2

In a small bowl, beat the cream cheese, sour cream, and vanilla with a hand mixer until smooth. Add the sugar gradually, continuing to beat until the mixture is smooth again.

Step 3

Beat in the egg until fully incorporated. Spoon out 2 tablespoons of the batter into a small bowl, then mix in the melted chocolate into the larger amount of batter.

Step 4

Divide the chocolate cheesecake batter among the ramekins. Spoon the reserved vanilla batter over the chocolate mixture and swirl a skewer or small knife through it to create a marble pattern.

Step 5

Add 1 cup of water to the inner pot. Place a trivet in the pot and then place the ramekins on top. If they won’t all fit in one layer, it’s fine to stack them. Drape a piece of foil over the ramekins to keep condensation off the top of the cheesecakes. Lock the lid in place.

Step 6

Select Pressure Cook or Manual, and adjust the pressure to High and the time to 6 minutes. After cooking, let the pressure release naturally for 8 minutes, then quick release any remaining pressure.

Step 7

Unlock the lid. Use tongs to remove the ramekins. Let cool for 20 minutes or so, then refrigerate to chill thoroughly, 3 to 4 hours