Create a sling for pan: Fold one 20-inch length of foil lengthwise into thirds. Place a 7-inch cake pan or cake-pan pressure-cooker insert over foil; transfer to a 6-to-8-quart cooker, holding foil sling in place. Fold tops of sling down, if necessary, to avoid interfering with cooker lid. Remove sling and cake pan from cooker.

Butter cake pan. Line with parchment, butter parchment, and sprinkle with 2 tablespoons sugar. Top with raspberries in an even layer. Whisk together flour, baking powder, salt, and remaining 1/2 cup sugar. In a large bowl, whisk together egg, milk, butter, zest, liqueur, and vanilla. Whisk flour mixture into egg mixture until just combined. Pour batter over fruit in pan, spreading evenly. Cover pan with foil.

Pour 3 cups water into cooker; set a 1-inch wire rack on bottom. Arrange foil sling under cake pan and set cake pan on top of rack.

Stovetop: Secure lid. Bring to high pressure over medium-high heat; reduce heat to maintain pressure and cook 30 minutes. Remove from heat and quickly release pressure, then remove lid.

Electric: Secure lid. Manually set cooker to 35 minutes and let it come to pressure. Once time is complete, turn off and quickly release pressure, then remove lid.

Use sling to remove cake from cooker; remove foil cover. Let stand 10 minutes. Run a knife around edge to loosen; invert cake onto a serving plate. Remove parchment and serve, topped with more berries and whipped cream.