Pour 2 cups of water into the inner pot the Instant Pot. Place the steamer rack in the inner pot, position handles upright.
Coat a round cake pan with cooking spray; sprinkle with 1 tablespoon of sugar, shaking gently to coat bottom sides of the pan.
Combine chocolate and butter in a small microwave-safe bowl. Microwave at high for 30-45 seconds, or until melted.
Lightly spoon flour into a dry measuring cup; level with a knife. Combine flour, cocoa and salt in a small bowl.
Beat egg whites with a mixer at high speed until soft peaks form; gradually add 2 tablespoons of sugar, beating until stiff peaks form.
Combine egg yolks and remaining 2 tablespoons of sugar in a large bowl. Beat with a mixer at high speed until thick and pale. Gradually beat in the liqueur, espresso granules, and the chocolate mixture.
Fold beaten egg whites into egg yolk mixture. Gradually sift flour mixture into egg mixture, and fold gently.
Spoon batter into prepared pan, spreading gently (do not deflate the batter). Cover with foil, making sure foil fits tightly around sides and under bottom of the pan. Carefully set the pan on rack in cooker.
Close and lock the lid of the Instant Pot. Turn the steam release handle to “Sealing” position. Select Manual function and set to cook on high pressure for 11 minutes.
When time is up, turn the cooker off. Open the cooker using quick pressure release. Remove the pan from the cooker using the rack handles.
Spoon warm cake into bowls, and serve immediately with ice cream. Top with chocolate shavings if desired.