Bring a medium pot of water to a boil. Put the egg yolks, sugar, and salt in a medium bowl and whisk to combine, then set the bowl over the boiling water. Cook, beating constantly with a handheld mixer or whisk, until the mixture is thick and pale yellow, 8 to 10 minutes.
Remove the bowl from the heat, whisk in the prosecco, and continue beating until the mixture cools to room temperature, about 5 minutes. Serve at room temperature or cold with the raspberries. (Store leftover zabaglione in an airtight container in the refrigerator for up to a day.)
