Step 1In the bowl of a food processor, pulse the flour, sugar and salt together to combine. Add the frozen butter cubes and pulse until the butter is reduced to pea-sized balls. Add the creme fraiche and pulse until mixed and the dough begins to form clumps.
Step 2Remove the dough and form into a coarse ball, then flatten to form a disk. Cover with plastic wrap and chill for at least 2 hours, preferably overnight.
Step 3Roll the dough larger than the diameter of the 10-inch tart pan, approximately 12 inches in diameter. Chill the rolled dough for 30 minutes, then carefully fit it into the pan, trimming and saving any leftover dough. Freeze the dough until ready to bake, at least 1 hour.
Step 4Heat the oven to 375 degrees. Line the inside of the tart shell with foil and beans or pie weights. Blind-bake the frozen shell until set and golden on the sides, 20 to 25 minutes; the dough will shrink a bit on the sides. Remove the weights and foil and continue to bake until the crust is fully set and a deep golden brown, an additional 10 to 20 minutes.
Step 5Cool on a rack, then chill the shell until ready to complete the tart (chill up to one day before baking).
Step 1Heat the oven to 350 degrees. In a small bowl, whisk the vanilla and rum into the creme fraiche.
Step 2In a heavy saucepan, combine the butter, maple syrup, brown sugar and salt over low heat. Cook, continuously whisking, until the butter is completely melted and the mixture comes together. Increase the heat to high and continue to cook until the mixture is frothy and bubbly. Continue cooking, whisking constantly, for 1 minute.
Step 3Remove from heat and slowly and carefully add the creme fraiche mixture, whisking until smooth. Continue whisking, adding the yolks, one at a time. Stir in the pecans.
Step 4Fill the cold tart shell with the filling just to below the top of the crust; you may have a little filling leftover. Bake until the top has developed a crust and the filling looks set, 20 to 25 minutes. Remove the tart from the oven and gently tap on the counter to release any air bubbles. Place on a rack to cool completely. Serve the cooled tart with whipped creme fraiche.