Heat up some water in a saucepan over medium-low heat. We will use this water bath technique to slowly and gently cook our egg mixture.

In a heat-resistant bowl suitable for a water bath, add the egg yolks, sugar and liqueur. Take a whisk and mix the ingredients together smoothly, but without over-mixing.

Once the water reaches a gentle simmer, place the bowl on top of the saucepan, but not touching the water.

Whisk steadily while monitoring the mixture as it begins to transform before your eyes. Initially it will become foamy, then it will gradually thicken as the bubbles disappear. Continuously whisk without pause to ensure no lumps form which could compromise the smooth texture.

When the mixture has thickened to the proper consistency, use a thermometer to check the temperature, aiming for approximately 83°C (181°F), the optimal point. If a thermometer is unavailable, watch the whisk and wait for the ribbons left behind with each stroke to indicate full development.

Serve the zabaione immediately while still warm, either hot or at a lower temperature. Enjoy alongside biscuits or chocolate for a delightful treat, perfect for holiday celebrations and gatherings.