To make crust, combine dry ingredients in a large bowl. Cut in butter until mixture resembles coarse bread crumbs. Add eggs and mix well with a fork until evenly moistened and crumbs stick together when pressed. Divide into two equal balls, wrap each tightly in plastic wrap, flatten slightly, and put in freezer for 1-2 hours.
When dough is frozen solid, grate it into fine crumbs using a box grater. Coat tart pans with nonstick spray or butter. Press crumbs evenly, approximately ½-inch thick, into six 5-or 6-inch tart pans with removable bottom, or 12 individual tart pans. Smooth crust edges and be sure to press dough out of corners of the pan.
Prick tart bottoms all over with a fork. Bake for 18-20 minutes, or until dough looks and feels slightly dry. If you are using larger 5-or 6-inch tart pans, the edges of the dough may start to come away from walls of pan. Cool tart shells completely, and remove from pans.
To make filling, use an electric mixer on high speed to cream chocolate hazelnut spread, cream cheese and butter. Slowly add sugar and beat until fluffy. Beat in vanilla. In another bowl, beat whipping cream until soft peaks form. Gently mix the whipped cream into chocolate-hazelnut cream cheese mixture.
Fill tart cups two-thirds full. Spoon the mousse into the tart and smooth it with spoon or knife, or pipe the mousse into the tart using a pastry bag or plastic bag with one corner removed. Cover tarts loosely with plastic wrap and refrigerate at least 1 hour. Garnish as desired with 1/2 teaspoon raspberry jam, preferably seedless, dark chocolate shavings, hazelnut halves, etc.
Notes: Keep refrigerated. Keeps up to 3-4 days refrigerated in sealed container.
Substitutions: Feel free to use any other nut butter instead of chocolate hazelnut. Peanut butter works very well, too.