Heat oven to 350 degrees F/180 degrees C For the pastry: Put the flour, sugar and salt in a large bowl. Add the butter pieces, and pinch with the fingers to create a crumb texture. Make a well in the middle, and add the eggs. Quickly work in the flour mixture to create dough. Do not over-mix. Pat into a disk and refrigerate 15 minutes before rolling out. Fit into a 9-inch tart pan. For the filling: Arrange the cherries in the crust. Beat the eggs with the sugar, and then stir in the creme fraiche and vanilla. Pour the custard over the cherries. Bake until set, about 25 minutes. Cool before serving.