The little KC kids are obsessed with jello. Like a lot of kids, the infatuation has more to do with the slip and jiggle than any particular flavor profile. I mean, when you assert preference by color, how important, really, is taste? I'm going with not very.
Disclaimer time. The original recipe calls for creme fraiche, which while picking up rhubarb and buttermilk at Whole Foods, I could have sworn was happily residing in my fridge just waiting to be called into action. Alas, when I got home, that very creme fraiche mysteriously had morphed into mascarpone! I hate when that happens. Fortunately there's almost always some Greek yogurt hanging around our house, which valiantly stood in for the mysterious traitor.
adapted from Bon Appetit
For the Panna Cotta
1 & 1/4 tsp unflavored powdered gelatin
1 & 1/4 cups heavy cream
1/3 cup granulated sugar
1/4 tsp kosher salt
1 vanilla bean, halved lengthwise
1 & 1/4 cups buttermilk
1 & 1/4 cups full-fat plain Greek yogurt
For the Sauce
1 & 1/2 cups (about 10 ounces) strawberries, hulled
1/4 cup granulated sugar
2 cups rhubarb, (about 8 ounces) sliced 1/4-inch thick
1/2 tsp unflavored powdered gelatin
For the Panna Cotta, pour 1/4 cup of cold water into a little bowl and sprinkle the gelatin over the top. Let is sit for about 10 minutes until the gelatin swells and softens.
In a separate small bowl, sprinkle the gelatin over 2 tablespoons cold water. Let it stand for 10 minutes.
While the gelatin is softening, bring the strawberry-rhubarb liquid to a boil in a small saucepan for about 3 minutes, stirring every now and then to prevent burning. Add the softened gelatin mixture and stir well to dissolve any stubborn gelatin granules. Remove from heat and let stand until completely cool.
Top the cold, set panna cotta with the cooled sauce and chill until the sauce is thickened, at least 2 hours.