Preheat oven to 375°. Lightly butter 2 large baking sheets. On a floured surface with a floured rolling pin, roll out pastry to 16 by 18 in. Cut pastry in thirds lengthwise and in half crosswise. With a wide spatula, transfer the 6 rectangles to baking sheets.
Core pears and cut into thin wedges. Arrange, slightly overlapping, on pastry rectangles, leaving a 1 1/2-in. border bare (angle slices if necessary). Warm marmalade in a microwave oven to melt, then brush over pears. Fold border over edge of pears, stretching slightly and pressing down to hold. Brush new edges with egg, then sprinkle turbinado sugar over tarts, especially pastry edges.
Bake until pastries are richly browned, 25 to 30 minutes. In a small bowl, whisk crème fraîche and granulated sugar until slightly thickened. Serve tarts warm or cool, with crème fraîche.