Prepare + chill crust

By hand: Whisk flour, salt and confectioner's sugar (and xanthan gum if gluten-free) in a large bowl.  Using tips of fingers, rub butter in until it looks mostly like wet sand.  Make a well in the middle, and pour in the beaten egg.  Gradually work the egg into the flour until a moist dough forms, using the heel of your hand to distribute any remaining large pieces of butter. Shape into a flat disk and cover with plastic wrap.  Refrigerate or freeze until firm throughout. This can be done 2-3 days ahead, or way in advance of the Yule Ball and frozen. Thaw until cold but soft before rolling.

In food processor: Processor flour, sugar, salt (and xanthan gum for gluten free) until combined. Add butter cubes, and pulse until large pieces are no longer visible. Add beaten egg, and pulse until dough comes together. Shape dough into flat disk, wrap tightly and chill for a couple hours, overnight, or freeze.

Roll + mold crust into pan

Between two pieces of parchment paper, roll out dough into circle a quarter of an inch thick, and at least an inch or two larger than your tart pan. Place dough in tart pan with a removable bottom, and press gently but firmly against the bottom and sides to secure dough.  Trim any excess dough hanging over the edges.  Place in refrigerator or freezer until chilled and firm throughout.

Dock + pre-bake crust

Preheat oven to 350° F.  Dock the bottom of the crust with a fork, lay a large, crumpled piece of parchment on top (or use foil), and pour in pie weights (or a pound of dried beans or even spare coins). Bake for 25 minutes on an inverted sheet pan, until crust is a light golden brown. 

Boil + mix treacle filling

1. While the pastry crust bakes, toast almond meal or bread crumbs in large pan until fragrant and light brown, stirring to keep bottom layer from burning. 
2. In a small saucepan, combine syrup, molasses, and salt, and bring just to a boil. Remove from heat and cool for 5 minutes. 
3. Whisk together eggs, heavy cream, vanilla, and ginger.
4. Whisk treacle mixture into egg mixture, then whisk in bread crumbs or almond meal. 

Ready, set, bake!

1. Take pastry crust out of oven and remove weights and parchment. Lower oven to 325° F.
2. Place tart pan back in oven on top of sheet pan.
3. Pour filling into crust. Bake for 30 to 40 minutes, or until filling is set in the center (when jiggled moves as one mass). 
4. Cool in the tart pan on a rack.