Pulse together cake flour, cocoa powder, sugar and salt in food processor. Add butter; pulse until mixture looks crumbly.
In small bowl, lightly beat together egg yolk and 1 tablespoon cold water. With processor running, add yolk mixture and process until dough begins to clump (add additional teaspoon water, if needed). Turn dough out onto work surface. Divide into fourths; shape each into a disk. Wrap; refrigerate 30 minutes.
On well-floured surface, roll 1 disk into 7-inch round. Fit into 4-3/4-inch tart pan with removable bottom. Repeat with the remaining 3 disks and 3 more tart pans. Place in freezer for 30 minutes.
Place baking sheet in oven. Heat to 350°F. Place tarts on baking sheet.
Bake in 350°F oven for 15 minutes. Transfer tart pans to wire rack; let cool completely.
In small heavy saucepan, heat cream until small bubbles appear around sides of pan. Place chopped chocolate in medium-size bowl. Add hot cream; stir until smooth. Let cool to room temperature. Add mascarpone cheese; beat until smooth.
Remove tarts from pans. Divide filling among tarts, spreading smooth. Top with the raspberries.