To bake the tart, line the rack under the one you plan to use with a sheet of aluminum foil to catch any spills and drips.
Heat the cream, sugar, and salt in a big, wide heavy-duty pot (use one that’s at least 4 qts, 4l) until it begins to boil.
Continue to cook and when it starts to foam up, remove it from the heat and stir in the almonds, the almond extract, and the liquor.
Scrape the filling into the shell. If there’s a bit too much filling, don’t toss it; in case the tart leaks, you can use it to add more.
Make sure there are no clumps or piles of almonds and that everything is evenly distributed, then put the filled tart shell into the oven.
After the first ten minutes, check the tart.
Take a heatproof rubber spatula, holding it diagonally and with a tapping motion, break up the surface of the tart. Doing this is very important since it avoids the top of the tart getting that ‘corn flaky‘ look.
Be sure to give the filling a good series of ‘taps’—not enough to break the tart shell pastry underneath, but it’s important to break up the surface crust that’s forming.
Continue to cook, checking the tart every 5-8 minutes, and break up any dry crust that may be forming, getting less aggressive as the filling sets up. As it begins to caramelize, stop tapping it and let the tart do its thing.
Remove the tart from the oven when the filling is the color of coffee with a light touch of cream in it and there are no large pockets of gooey white filling, about 30 minutes. Let the tart cool a few minutes on a cooling rack.
Check and see if the tart has fastened itself to the tart ring. Slide a knife (or a curved vegetable peeler, which will slide nicely in between the ridges) between the tart and the pan to loosen it so the sides don’t come off when you remove the ring.
To remove the ring, rest the tart on top of a solid object (like a tall jar) and gently coax the ring off. Slip a large spatula underneath it to return the tart to a cooling rack.
Once completely cool, run a long chef’s knife under the tart to release it from the bottom. If it’s stubborn, set the tart on top of a warm stove burner for a second or two and you should be able to pry it off.