Unwrap your larger round of dough and place on a lightly floured work surface. Roll the dough to about 1/8inch (12-13 inch diameter). Use flour as needed to keep it from sticking.
It's easiest to transfer your dough by folding it into quarters. Pick up the folded dough, and place in your tart pan, and unfold gently. Pat the dough into the sides of the pan, and trim the overhang to 1/4inch. Cover in saran and refrigerate until ready to fill.
Unwrap your smaller round of dough and place on a lightly floured work surface. Roll the dough to about 1/8inch (10-inch diameter). Use flour as needed to keep it from sticking. Transfer to a parchment lined baking sheet or large cake cardboard. Cover in saran and refrigerate until ready to fill.
Preheat your oven to 375 deg F (191 deg Celcius).
Place your saucepan over med-low heat, and add sugar and water. Stir until sugar is fully dissolved, 3 minutes.
*This is the trickiest step, please proceed carefully.* Once the sugar is dissolved remove the whisk, and clean the sides of your bowl of any crystals with a wet pastry brush. Then, raise the heat to med-high and bring it to a boil, without stirring, until it reaches a medium dark amber color (340-350 deg F, 170-191 deg C). If you see crystals forming around the edges of your pot, use a wet pastry brush to wipe them down, or your sugar can seize.
As soon as the sugar reaches temperature (or color), remove it from heat and add your cream (it will bubble up like crazy). The addition of the cream (especially if cold) may cause it to seize - don't panic! It'll melt back down over heat. Just keep going, trust me. Once the bubbling settles, add the honey and butter, and return the pan to medium heat. Stir until the mixture is smooth, then continue to cook until it reaches 238 deg F (114 deg C), about 10 min.
Remove the pan from heat and add the pecans, vanilla extract, and salt, stirring to combine.
Remove your dough rounds from the refrigerator. Place your tart pan onto a baking sheet. Pour the pecan filling into the tart shell and use a rubber spatula to spread it evenly. Transfer the other pastry round over the top of the tart. If needed, trip the edge of the dough so it fits inside the tart pan.
Make your starch water by mixing the cornstarch and water. Brush the overhanging edge of your bottom dough with the starch water, then fold over the top of the tart and press gently to seal.
Using a small knife, cut a 1-inch steam vent in the top crust. Place the baking sheet in the oven and bake until the pastry is cooked through. **Dahlia's recipe cites 50-55 minutes baking time, but mine was done in 30 minutes. Watch your oven carefully, and pull your tart out when your crust is a beautiful golden brown.
Once baked, put the tart pan on a wire rack to cool for about an hour. Then, remove the sides of the tart pan, and invert onto a 9-inch cake cardboard (or a large flat plate). Remove the metal bottom of the pan from the top of your tart. Place back on the wire rack to cool for at least 3 more hours (or, if you prefer, let it rest at room temperature overnight -- this is my preference).