Using a stand mixer with the paddle attachment, cream the butter and sugar.
Add the yolk and mix well.
Add the salt and flour and mix until no flour is discernible, scraping down the sides at least once. The dough should come together when pinched. If it seems too dry, add the milk and mix it through.
Dump the dough onto a sheet of plastic film or waxed paper, then wrap it tightly to bring it together into a ball; refrigerate for 1 hour.
Preheat the oven to 400°F/200°C.
On a lightly floured surface, do your best to roll the dough into a 12 to 13-inch circle.
Transfer the dough to a 10-inch tart pan with a removable bottom (I used a 10-inch springform pan); I assure you that it will break and tear. This dough (also known as pâte sablée) is very forgiving!
Press the dough into the sides and bottom, trimming the edges and filling any crackers or tears with leftover dough. You can see how I constructed the sides first. I then added pieces of rolled-out dough to create a patchwork bottom, pressing it together and making it even using the bottom of a glass.
Line the dough with parchment or foil and fill with pie weights or dried beans.
Bake for 15 minutes then remove the lining and weights and bake 10 minutes longer until golden. Remove from the oven and set aside to cool.
Reduce oven temperature to 350°F/180°C.
When the crust is cool, whisk together the jam and lemon zest and spread it on the bottom of the crust. It should be an even layer about 1/4-inch thick.
Whisk together the topping ingredients until smooth. Pour over the fig filling and bake for 20-25 minutes, until set.
Remove from the oven and let cool to room temperature prior to serving.