In a mixing bowl, combine all-purpose flour and salt, whisking them together thoroughly. Cut in the unsalted cold butter until the mixture resembles coarse crumbs. Mix in the crème fraîche and cold ice water until a thick dough forms. Wrap and chill for 1 hour.

Preheat your oven to 400°F (200°C). Line the chilled tart crust with parchment paper and fill with pie weights. Bake for 20-25 minutes, then remove weights and bake for another 10 minutes until lightly golden. Let cool on a wire rack.

In a skillet over medium heat, cook the bacon until crispy, then chop it. In the same skillet, add sliced onions and sauté for 10-15 minutes until translucent.

In a mixing bowl, whisk together eggs, crème fraîche, and black pepper until smooth. Fold in the cooled onions and chopped bacon.

Pour the filling into the cooled crust and bake for 40-45 minutes until set and golden. Check for doneness at 35 minutes.

Allow the tart to cool on a rack for about 30 minutes. Serve warm or at room temperature.