Preheat oven to 350 degrees; make sure there's a rack in the center.
For the shortbread, sift the flour, salt and sugar into a bowl.
Add butter to the flour mixture, stirring with a fork until combined into a soft ball. Gently pat dough into a 9-inch square baking pan. Prick the dough all over with a fork and bake for 20 to 30 minutes, or until golden brown and dry. Set aside to cool.
For the caramel, combine the sugar and water in a medium saucepan and bring to a boil over medium-high heat. Swirl, DO NOT STIR, occasionally until the sugar has melted. Continue to simmer for about 10 minutes, still swirling occaisionally, until it turns a dark amber color. DON'T LET IT GET overly dark, as it will taste burned.
As soon as the sugar reaches the right color, remove from the heat and carefully add the cream, whisking constantly. The mixture will bubble up furiously as you do this, so be careful. Whisk in the butter a piece or two at a time until melted in and then add the crème fraiche. Set aside to cool for about 15 minutes, stirring occasionally.
When the caramel is cool enough to touch, pour it evenly over the shortbread. Tap pan gently on the counter to remove any bubbles. Refrigerate while making ganache.
To make the ganache, bring the cream just to a boil in a small saucepan. Remove from the heat, and whisk in the chocolate chips until smooth and shiny. Let cool until slightly thickened (about 5 minutes), and pour evenly over the caramel, again tapping it against the counter to remove bubbles. Let it sit at room temperature until the chocolate starts to firm up a little (15 minutes or so), then sprinkle the top with salt and refrigerate for 3-4 hours or until quite firm. Cut into small squares and serve while still chilled.