Preparation

Make the crust:

• In a stand mixer fitted with the paddle attachment, combine the flour, sugar, salt and butter and mix on medium speed until the butter blends into the flour and the mixture resembles a coarse meal. Mix the cream and yolk together in a small bowl. With the mixer on low speed, gradually add the cream mixture and mix until just combined. Do not overwork the dough.
• Transfer the dough to a work surface and bring it together with your hands. Shape the dough into a 1-inch-thick disk. If the dough seems too soft to roll out, put it in the refrigerator for 5 to 10 minutes to firm it up a little. Set the dough on a lightly floured work surface, sprinkle a little flour over it, and roll it out into a 1/8-inch-thick circle 14 to 15 inches in diameter, reflouring the dough and work surface as necessary.
• Starting at one side, roll and wrap the dough around the rolling pin to pick it up. Unroll the dough over an 11-inch fluted tart pan with a removable bottom
  and gently fit it loosely in the pan, lifting the edges and pressing the dough into the corners with your fingers. To remove the excess dough, roll the rolling pin lightly over the top of the tart pan, cutting a nice, clean edge. Cover loosely with plastic and chill for 1 hour.

Make the tart:

• Position a rack in the center of the oven and heat the oven to 375ºF.
• Prick the bottom of the crust with a fork and line it with a piece of parchment paper or several opened-out basket-style coffee filters. Fill the lined tart shell with dried beans or pie weights and bake until set around the edges, about 15 minutes. Take the tart out of the oven, and carefully lift out the paper and pie weights (if using coffee filters, spoon out most of the weights first). Return the tart to the oven and bake until the crust is golden brown all over, another 10 to 15 minutes. Cool completely on a rack.
• While the crust is baking, spread the nuts on a baking sheet and toast (in the same oven) until they are golden brown and smell nutty, 10 to 12 minutes. Let them cool, and then chop coarsely.
• In a small pot, bring 3/4 cup of the cream and the butter to a simmer. Set aside.
• Combine 1 cup of the sugar with the corn syrup, vanilla bean seeds and pod, and 1/4 cup water in a 3 or 4-qt. heavy-based pot. Boil over high heat, stirring frequently with a wooden spoon, until the mixture becomes caramel-colored. Remove from the heat and immediately (but slowly and carefully; you don’t want the hot sugar to overflow or splatter) whisk in the hot cream mixture.
• Pour the caramel into the baked tart shell and pick out the vanilla bean halves with a fork or tongs. Sprinkle about two-thirds of the macadamia nuts on top of the caramel. Let cool completely in the refrigerator.
• When the tart is cool, put the chocolate in a large bowl. In a small pot, bring 1/2 cup of the cream, the milk, and the remaining 1-1/2 Tbs. sugar to a boil over  medium-high heat. As soon as it boils, pour it over the chocolate. Let stand for 2 minutes and then stir very gently with a whisk until smooth and thoroughly combined. Let cool at room temperature for 5 minutes and then pour the chocolate filling over the completely chilled tart, covering the nuts and caramel.
• Chill in the refrigerator for at least 4 hours or until completely set. Unmold the tart, using a long thin metal spatula to release it from the pan bottom. Place it on a cutting board or a serving plate, depending on how you intend to serve it.
• Just before serving, whip the remaining 3/4 cup cream and the crème fraîche to soft peaks. Slice and plate the tart in the kitchen or at the table. Top each serving with a dollop of the whipped cream and scatter the remaining macadamia nuts over and around.

Make Ahead Tips

You can roll out and freeze the tart dough up to a week in advance. Defrost in the refrigerator overnight before baking.