How to Make It
Preheat oven to 425°F.
Line a rimmed baking sheet with parchment paper. Combine plums, butter, and 1 1/2 tablespoons sugar in a bowl; toss well to coat. Arrange plum mixture on prepared pan; bake at 425°F for 15 to 17 minutes or until plums begin to soften and release their juices. Remove pan from oven; cool slightly.
While plums roast, bring sherry to a simmer in a small saucepan over medium heat. Simmer 8 minutes or until reduced to about 2 tablespoons. Add vinegar to pan; cook 12 minutes or until mixture is reduced to about 1/4 cup, stirring occasionally. Remove pan from heat. Stir in remaining 1 1/2 tablespoons sugar and vanilla. Cool 5 minutes or until slightly thickened.
Place about 1/2 cup plums in each of 6 shallow bowls. Top each serving with 1 tablespoon crème fraîche and 2 teaspoons vinegar mixture.