Pastry Dough

For the pastry dough, place the flour, vanilla powder, and sugar in the work bowl of a food processor fitted with a steel blade. Cut the butter into pieces and add. Pulse the mixture using on/off turns until the butter is cut into very tiny pieces, about 1 minute.

Combine the egg yolk, cream, and vanilla extract in a small bowl. With the machine running, pour the liquid through the feed tube. Process the dough until it forms a ball, about 1 minute. Gather the dough into a disc, cover with plastic wrap and chill for at least 1 hour, until firm.

Center a rack in the oven and preheat to 350F (175C). Roll out the pastry on a lightly floured smooth work surface to a 14 inch circle, about 1/8 inch thick. Gently roll the pastry around the rolling pin and unroll carefully into the tart pan. Lift up the sides of the pastry and fit against the bottom and sides of the tart pan. Trim off the excess pastry at the top. Line the pastry with a large piece of foil and weight with tart weights. Place the tart pan on a jelly-roll pan and bake for 10 minutes. Remove the foil and weights and bake for another 10 to 12 minutes, until the shell is light golden and set. Remove from the oven and cool on a rack while preparing the filling.

Filling

Place the brown sugar, granulated sugar, light and dark corn syrup, eggs, egg yolks, and vanilla extract in a mixing bowl together. Whisk together until light, about 1 minute. Set aside briefly.

Place the butter in a small saucepan. Using a sharp knife split the vanilla beans lengthwise, scrape out the seeds, add both the vanilla beans and seeds to the butter, and brown over medium heat. This will take about 3 to 4 minutes. Remove the vanilla beans and add the butter to the sugar mixture. Blend in the macadamia nuts and pour the mixture into the pastry shell.

Bake the tart in the preheated oven for 30 minutes, until set and golden colored. Remove from the oven and cool on a rack for 30 minutes, then remove the sides of the tart pan. The tart is best served within 4 hours, but will last for up to 3 days tightly covered in the refrigerator.

For the garnish, whip the cream in the bowl of a stand mixer using the wire whip attachment or in a mixing bowl using a hand-held mixer, until it is frothy. Add the sugar and vanilla and continue to whip the cream until it holds soft peaks. Serve a dollop of whipped cream on top of each slice of tart.