Place the egg yolks in a bowl preferably unlined copper.
Place the bowl over a saucepan of simmering water. It is important that the bottom of the bowl not touch the water.
With a whisk beat the egg yolks until they are frothy, then gradually beat in the marsala and sugar. Continue beating about 5 minutes longer, until the zabaglione mixture is hot, just beginning to give off steam, very light, frothy, and thick.
Remove the bowl from the heat and continue beating until the mixture has cooled to room temperature.
To serve, divide the raspberries among 4 shallow flameproof molds, such as creme brulee molds.
A single larger mold, such as an 8-inch (20-cm) porcelain quiche dish, can be used instead.
Preheat a broiler. Spread the zabaglione mixture over the raspberries into the mold or molds and place under the broiler for about 30 seconds, until the top has browned lightly. Serve at once.