Cut a piece of parchment paper that is the size of the bottom of the 7-inch springform pan and place in the pan. Spray the parchment paper and the inside sides of the pan with cooking spray.
Process the chocolate wafers in a food processor until fine, or place in a large baggie and crush with a rolling pin.
Add the crushed wafers to a small bowl and add 1 tablespoon sugar and the melted butter. Stir to incorporate.
Press the crumbs evenly on the bottom of the springform pan and up about 1 inch along the sides of the pan. Place in the freezer while you prepare the filling.
In a medium microwave-safe bowl, melt the chocolate chips on high, stirring every 30 seconds, until completely melted. Set aside.
In a large bowl, use an electric mixer on medium speed and beat the cream cheese together with the 3/4 cup sugar until smooth and fluffy (about 2 minutes).
Add the eggs one at a time, beating well after each addition.
Beat in the sour cream and vanilla.
Remove 1/2 cup of the cream cheese mixture and place in a small bow.
With the mixer on low speed, pour the chocolate in and mix thoroughly.
Pour the filling into the prepared crust.
Dollop the reserved cream cheese mixture across the top of the of the cheesecake and use a knife to swirl the cream cheese mixture with the chocolate mixture to give a marbled look.
Tightly wrap the entire pan in aluminum foil.
Using another piece of foil that is 24 x 3 inches long and make a 'sling' by folding it in half, length wise, and then fold in half two more times.
Place the steam rack (that came with the IP) into the Instant Pot and add 1 1/2 cups water.
Place the cheesecake on the sling and use the sling to lower the pan onto the steam rack and gently fold the sides of the sling over the top, careful not to press into the cake.
Lock the lid and press PRESSURE COOK or MANUAL and cook on HIGH PRESSURE for 55 minutes.
Use the QUICK RELEASE method to vent the steam (be careful of the escaping steam), and then open the lid once finished releasing.
Use the sling to lift the pan out of the Instant Pot (be careful, it will still be hot).
Remove the foil and let cool on a rack for 30 minutes (the center will still seem wobbly at this point).
Run a knife around the edges to loosen the cake from the pan and remove the sides of the springform pan.
Refrigerate for at least 6 hours or overnight.
Serve with chocolate sauce
, if desired.