Preheat the oven to 375°F (190°C).
Place the spelt flour, salt, butter, and lemon zest in a food processor and pulse until it resembles breadcrumbs. Add the ice water and heavy cream, and process until moist clumps form.
Gather the dough into a ball and knead it for a minute on a lightly floured surface. Transfer to a plate and cover with plastic wrap. Refrigerate for 30 minutes.
On a floured surface, roll the dough ball into a disk larger in diameter than your tart pan (I used a 9-inch tart pan with a removable bottom for this recipe). Line the pan with the dough: on the base and up the sides. Trim the excess and prick the base with a fork. Refrigerate for 30 more minutes.
Remove from the refrigerator and line with foil with edges hanging over the sides of the tart pan. Fill it with pie weights, uncooked rice, or beans, etc.
Bake the crust for 20 minutes until the pastry begins to turn light brown. Discard the foil and weights and bake for another 5-10 minutes, until it is dry and the bottom turns lightly golden.
Remove from the oven and let cool completely before adding the filling.