Cut each sheet of phyllo in half lengthwise to make two 17 x 6 inch sheets.
Lay one piece on work surface, keeping remainder covered with plastic wrap and damp towel. Brush lightly with butter; top with another piece so edges are not perfectly aligned and all eight corners are visible. Repeat with remaining phyllo.
Gently fit into 14 x 4 inch tart pan with removable bottom. Turn edges under and ruffle, allowing some to hang over edge. Line with foil; fill with pie weights or dried beans. Bake in center of 375°F oven for 10 minutes; remove weights and foil. Prick shell all over with fork; bake for 5 minutes or until golden. Let cool on rack. Remove from pan and place on serving platter.
In bowl over saucepan of hot not boiling water, melt chocolate, stirring occasionally. Spread about two thirds over crust.
Slice 1 cup of the strawberries; arrange over chocolate. Beat together mascarpone, 18% cream, sugar and vanilla; spread over strawberries. Halve remaining strawberries; arrange cut side down, over filling. Drizzle with remaining chocolate. Makes 8 servings.