Preheat oven to 375 degrees F.
Combine crust ingredients until well mixed.
Press into bottom and up sides of tart pan (or up about 1” of springform pan.)
The shell may be made ahead and refrigerated until ready to fill.
1. Make caramel by bringing to a boil over low heat margarine (or butter) and brown sugar.
Stir frequently until it sticks to spoon or whisk.
Mixture will be thick and syrupy.
Pour caramel evenly over crust.
Sprinkle hazelnuts evenly over crust.
To make chocolate filling, combine chocolate and margarine (or butter) and gently melt over simmering water or in the microwave, stirring to combine.
Stir together eggs, yolk, sugar and vanilla in a stainless steel bowl. (Warning: Do not allow the bowl to become hot over the simmering water before adding eggs or your eggs will cook!)
Heat over simmering water only until the point that sugar has just dissolved (no longer or eggs will cook), stirring constantly with a spatula (not a whisk).
Do not incorporate air into mixture.
Remove from heat and fold in chocolate mixture.
Sift cake meal over bowl and fold in.
Chocolate filling may be made up to 4 hours ahead, and kept covered at room temperature.
Pour chocolate filling carefully over hazelnut layer.
Bake for 12-14 minutes OR until edges of filling puff.
Center will be slightly soft.
Cool at least 15 minutes before removing from pan.
May be served warm or at room temperature.