Combine the water and vanilla and work it into the flour-butter mixture just until the pastry is blended and will hold together if you press it. Gather it into a ball and wrap it in plastic. Let it rest for 30 minutes so the flour will absorb the moisture more completely. At this point you can wrap the pastry in foil and freeze it for up to a month.
Pinch off a small piece of dough and set it aside for patching. Press the remainder of the pastry into a 9-inch tart pan with a removable bottom. Do not use a black one; the shell might burn if you do. Make sure that you have a layer of even thickness over the bottom and the sides. If the thickness is uneven, some parts will bake too much before other parts are cooked. Wrap the shell in foil and freeze for 30 minutes or overnight.
When ready to bake, preheat the oven to 375 degrees. Unwrap the shell and place it in the oven (you don't need to fill the shell with weights because it doesn't shrink much) for about 25 minutes, or until light golden brown and baked all the way through.
Remove from the oven and let cool on a rack while preparing the filling. Increase the oven temperature to 400 degrees.
For the tart: Mix the cream, 3/4 cup sugar, Grand Marnier, almond extract and pinch of salt in a saucepan large enough for the mixture to triple in volume, stirring well. Heat until it comes to a rolling boil and bubbles thickly, stirring occasionally. Remove from the heat, stir in the almonds, and let stand for about 15 minutes.
Meanwhile, patch the tart shell if necessary. Use an offset spatula to smooth a small piece of very soft reserved dough over any crack that looks as if it goes all the way through the shell. Be careful not to break through the crisp top of the baked crust if you can avoid it; if the filling leaks through, it will caramelize on the bottom of the shell. This is a necessary step, well worth the time.