Step 1

Preheat oven to 325°F. Stir together 3 cups flour and salt in a medium bowl. Grease and flour a 10-inch (10- to 15-cup) Bundt pan. Set both aside.

Step 2

Place sugar and butter in bowl of a stand mixer fitted with the paddle attachment; beat on high speed until light and fluffy, 5 to 6 minutes. Reduce speed to medium, and add eggs, 1 at a time, beating until fully incorporated after each addition and stopping to scrape down sides of bowl after every 2 eggs. With mixer running on low speed, add flour mixture in 3 additions alternately with heavy cream, beginning and ending with flour mixture. Stir in crème fraîche and vanilla.

Step 3

Toss together chestnuts and remaining 2 tablespoons flour until well coated. Spoon half of batter into prepared pan; top with chestnuts. Add remaining batter, and smooth top. Tap cake pan on work surface to release any air bubbles. Bake in preheated oven until golden brown and a wooden pick inserted in center comes out clean, 1 hour to 1 hour and 20 minutes. Cool cake in pan on a wire rack 10 minutes. Invert cake onto wire rack, and let cool completely, about 2 hours.

Step 4

To serve, transfer cake to a heatproof rimmed serving platter. Place Cognac in a heatproof measuring cup with a spout. Heat a small saucepan over medium until warm, about 30 seconds. Remove saucepan from heat, turn off burner, and pour in Cognac. Using a long match or lighter, carefully ignite fumes just above surface of Cognac. Slowly and carefully pour flaming liquid over cake. Allow flames to extinguish before slicing and serving.