Published July 1, 2009.
Baking berries and custard into a gratin should yield firm but juicy fruit, a creamy topping, and a crisp crust—if the heat doesn’t ruin the plan.
This dessert is made by spreading fruit in a shallow vessel, covering it with a topping, and baking until the fruit releases its juices and the topping turns crisp and browned. Our favorite topping is the ethereally light and foamy Italian custard called zabaglione. However, while the custard is whisked together from just three ingredients—egg yolks, sugar, and alcohol—the whisking is done over heat and it requires constant watching so that the mixture doesn’t overcook. It also needs to be whisked just long enough to transform the egg yolks to the ideal thick, creamy, and foamy texture. Heat also proves a little tricky for the berries. Too much and they turn soupy and lose fresh flavor; too little and they barely warm through.
Juicy, firm berries covered in frothy zabaglione and topped with a lightly browned crust.
We chose to make individual gratins for entertaining and settled on raspberries, strawberries, blueberries, and blackberries. We first wanted to finesse the gratin assembly and baking steps before tweaking the zabaglione preparation and flavor. We tossed the berries with sugar and a pinch of salt to draw out their juices and let the mixture sit until some of the flavorful liquid began to seep out. We then topped the juicy berries with the custard and broiled the gratins for a few minutes. Success: The custard was golden brown, and the berries were warmed through, with just the right succulent texture.
For the zabaglione, we made three small but significant tweaks to foolproof the technique. First, to ward off scrambled yolks, we turned down the heat slightly, keeping the water beneath the custard bowl to barely a simmer. Second, we used a thick, heatproof glass bowl instead of a metal bowl for even, gentle cooking, as metal conducts heat more quickly, making the custard more likely to overcook. Finally, to get the right texture, we didn’t stop whisking when soft peaks formed; instead we waited until the custard became slightly thicker, similar to the texture of hollandaise sauce.
As for flavor, tasters thought that zabaglione made with Marsala was a bit sweet and cloying on top of the berries. We switched to a crisp, dry Sauvignon Blanc and found that its clean flavor allowed the berries to shine. However, with that change, no matter how long we whisked, our zabaglione was so frothy, it verged on runny. We tried adding more sugar to stabilize the zabaglione, but that made it achingly sweet. It was time to introduce another thickening element. After trying cornstarch and gelatin with disappointing results, we turned to whipped cream. After carefully folding in a few tablespoons of whipped cream into the cooked and slightly cooled zabaglione base, we spooned it over the berries. Finally, we had a light, smooth, and creamy concoction cut with a touch of dry white wine. The only thing missing was a slight crunch. Sprinkling the custard with a mixture of brown and white sugar before broiling created a crackly, caramelized crust.
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