Combine the rhubarb, strawberries, sugar, and water in a medium saucepan. Cook over medium heat for about 10 minutes, until very soft and broken down into a jam-like sauce. Stir in the vanilla extract and set aside to cool completely.
In a large bowl, beat the crème fraîche, heavy cream, powdered sugar, and vanilla extract until soft, fluffy peaks form — don’t overmix, or it will turn to butter.
In individual dessert glasses (so the layers show), spoon in a layer of cooled compote, then a layer of the whipped crème fraîche cream. Repeat until you reach the top.
Refrigerate for at least two hours to let the flavors settle. Just before serving, top with extra sliced strawberries and a few mint leaves.