To make the crust, lightly spray the sides and bottom of an 8-inch springform pan with a non-stick baking spray. Combine cookie crumbs, granulated sugar, and butter until it resembles the consistency of wet sand. Press mixture into the bottom and about ¾ inches up the sides of the pan. Place crust in the freezer while preparing the filling.
To make the chocolate filling, on medium speed in an electric mixer, combine cream cheese, milk, and sugar until light and fluffy. Add in eggs, one at a time, mixing until combined after each. Add in vanilla extract and flour and combine. Place the espresso powder and chocolate chips into a microwave-safe bowl or measuring cup and melt. Cool to room temperature. Pour into the filling mixture and combine on low speed until well-blended. Pour into your prepared pan.
To make the marshmallow swirl filling, combine cream cheese and sugar until fluffy. Mix in marshmallow fluff. Add in 1 tbsp milk and vanilla. Add in egg and mix just until combined. Mix in flour. Spoon marshmallow filling in dollops over the top of chocolate filling and swirl with a butter knife.
Cover cheesecake with foil, sealing edges. Pour 1½ cups water into the bottom of the Instant Pot. Place cheesecake on the trivet and lower into the Instant Pot. Seal and set to 55 min. at high pressure. After the time is up, allow to remain in the Instant Pot for 10 minutes, then release manually and remove to a wire rack to cool completely. After cooled, remove from pan and place on a serving plate if using a baker's torch to toast meringue or on an oven-proof plate or pan if toasting in the oven.
To make the topping, whip egg whites and salt until soft peaks form. Add the marshmallow cream and continue beating at high speed until stiff peaks form. Spread over cheesecake and brown with a baker's torch or under the oven broiler. Chill completely in the refrigerator before serving. A knife dipped in hot water and dried will help you be able to slice it better.