Prep the fruit. Combine sliced stone fruit with sugar, lemon zest, and citrus juice in a bowl. Add vanilla or liqueur if using. Toss gently and let sit 20–30 minutes, stirring once or twice, until a syrupy juice forms.

Set up a double boiler. Fill a medium saucepan with an inch or two of water and bring to a gentle simmer. Place a heatproof bowl on top, making sure the bottom doesn’t touch the water.

Whisk the base. In the bowl off the heat, whisk egg yolks, sugar, salt, and Marsala until combined and slightly lighter in color, about 30 seconds.

Cook and aerate. Set the bowl over the simmering water. Whisk constantly, reaching all around the bowl. In 6–8 minutes, the mixture should triple in volume and thicken to a ribbon that holds briefly when dripped. Adjust the heat so it steams, not boils.

Flavor to finish. When thick and glossy, remove from heat. Whisk in vanilla or lemon zest if using. Taste and adjust with a pinch more sugar or a squeeze of lemon if desired.

Assemble. Spoon macerated fruit and juices into glasses or shallow bowls. Top with warm zabaglione. Garnish with crushed amaretti and mint, or a dollop of barely sweet whipped cream.

Serve immediately. Zabaglione is best warm from the bowl with cool fruit underneath for contrast.