9 whole chocolate graham crackers
4 tablespoons (1/2 stick) unsalted butter, room temperature, divided
1 tablespoon honey
1 cup whipping cream
12 ounces bittersweet chocolate chips
1 tablespoon unsweetened cocoa powder
Preheat oven to 350 degrees. Spray 9-inch tart pan with removable bottom with non-stick cooking spray. Grind graham crackers with 3 tablespoons butter and honey in processor until fine crumbs form. Press crumbs evenly onto bottom (not up sides) of prepared tart pan. Bake until set, about 10 minutes. Cool.
Bring cream just to a boil in small saucepan. Reduce heat to low and simmer 5 minutes. Place chocolate in medium saucepan. Pour hot cream mixture into saucepan with chocolate. Stir over medium-low heat just until melted and smooth. Add cocoa powder and remaining 1 tablespoon butter; stir until melted and smooth. Pour chocolate mixture over crust in tart pan. Chill at least 45 minutes (chocolate will be slightly soft after 45 minutes and firm after 2 hours). Cut into wedges and serve.
Note: Can be made 1 day ahead. Cover and keep chilled. Let stand at room temperature 1 hour before serving.