Make crust: combine almond flour and salt. Cut in cold butter until crumbly. Add egg and mix until dough forms. Press into 23cm tart tin. Refrigerate 20 minutes.
Preheat oven to 190°C. Blind-bake crust 10 minutes with parchment and weights. Remove weights, bake 5 more minutes.
Fry lardons until golden but not crispy. Drain on paper towel.
Whisk eggs, cream, and crème fraîche together. Season generously with salt, white pepper, and nutmeg.
Scatter lardons and three-quarters of Gruyère over the crust.
Pour in custard mixture. Top with remaining Gruyère and thyme.
Bake 30–35 minutes until custard is just set with a slight wobble in the center. Rest 15 minutes before serving.