Preheat oven to 375 degrees F.
To prepare the crust, place macadamia nuts in the bowl of a food processor; pulse until finely ground.
Add flour and powdered sugar and pulse until combined.
Sprinkle cubes of butter over top. Pulse until just combined; drizzle in cold water and pulse one or two more times or until evenly moistened.
Dough will be crumbly, but should come together when pinched with your fingers.
Dump dough into a 9-inch-round or 4-by-15-inch rectangle tart pan with removable bottom. Firmly press dough into the bottom and up the sides of the pan.
Bake for 11 to 13 minutes or until edges are lightly golden brown.
Remove from oven and place on a wire rack to cool slightly while you prepare the filling.
In a medium saucepan, whisk together the eggs and egg yolks.
Whisk in the sugar until combined, followed by the lemon zest, lemon juice, and salt.
Add the butter and cook over medium-low heat, stirring constantly, until the mixture thickens slightly and reaches 170 degrees, about 5 minutes.
Pour the mixture through a fine-mesh strainer and into a heat-proof bowl; stir in the heavy cream.
Pour the filling mixture into the warm tart shell.
Place on a baking sheet and bake until the filling is shiny and opaque and the center jiggles slightly when shaken, about 10 to 15 minutes.
Remove from oven and allow to cool completely to room temperature, about 1 1/2 hours, then refrigerate until ready to serve.
