Recipe by Sarah Karnasiewicz
Start to Finish: 1 hour (plus 7 hours for chilling)
3/4 cup sugar
6 tsp. unflavored gelatin (from three 1/4-oz. packets)
4 cups half-and-half
1 cup plain whole-milk yogurt
1 tbsp. pure vanilla extract
1/8 tsp. kosher salt
1 vanilla bean, split lengthwise, or 1 tbsp. pure vanilla extract
3 lb. sliced frozen strawberries
2 cups sugar
8 1/2 tsp. unflavored gelatin (from four 1/4-oz. packets)
1. For the panna cotta, in a large bowl, whisk the sugar and gelatin. In a small saucepan, heat 1 1/2 cups half-and-half over medium-low just until it starts to simmer. Add to the large bowl and whisk constantly until the sugar and gelatin completely dissolve, 2 to 3 minutes. Add the remaining 2 1/2 cups half-and-half, the yogurt, vanilla extract, and salt. Scrape in the seeds from the vanilla bean and whisk until blended. Pour into a 12-cup gelatin ring mold (one with a simple pattern) and refrigerate until set, about 6 hours.
2. For the strawberry gelatin, in a large bowl, toss 2 lb. strawberries and 1/2 cup sugar. Let stand at room temperature until the berries soften and release juices, about 2 hours. Using a fine-mesh strainer, strain the berries over a large bowl. Add the berries to a large saucepan. Reserve the juices.
3. Add the remaining 1 lb. strawberries and 3 cups water to the berries in the saucepan. Bring to a low simmer. Cook, occasionally stirring gently and skimming off any foam, until the syrup is deep red and the berries have lost color, about 20 minutes. Using a fine-mesh strainer, strain the syrup into a medium bowl. Pour the syrup back into the saucepan; discard the berries. Add the reserved juices to the saucepan. Bring the syrup to a simmer over low heat.
4. In a large bowl, whisk the remaining 1 1/2 cups sugar and the gelatin. Whisk in the hot syrup. Whisk until completely dissolved, 1 to 2 minutes. Let cool to room temperature.
5. Fill a sink with about 1 inch of lukewarm water. Place the mold in the sink and let stand just until the panna cotta loosens from the mold, 10 to 30 seconds. Using your fingertips, gently loosen the panna cotta from the sides, center, and bottom of the mold. Pour the strawberry syrup down the sides and center of the mold so it flows underneath the panna cotta. (The panna cotta will float up.) Refrigerate until completely set, at least 4 hours.
6. Fill a sink with about 1 inch of lukewarm water. Place the mold in the sink and let stand just until the gelatin loosens from the mold, 10 to 30 seconds. Using your fingertips, gently loosen the gelatin from the sides of the mold. Invert the gelatin onto a platter and cut into slices.