1
Preheat the oven to 375° F.
2
Combine the flour and the butter in a stand mixer with the paddle attachment. Mix on low until the butter is mostly incorporated, but some small pea size pieces of butter remain, about 3 minutes.
3
Combine the vinegar and the water. With the mixer running, slowly add the water until the dough comes loosely together, adding a bit more water if required. Do not over-mix as the dough should not be sticky. Pour the dough onto a piece of plastic wrap and shape into a disk. Cover and refrigerate for 20 minutes.
4
Strip the stems from the Swiss chard and rinse in cold water. Add the wet Swiss chard leaves to a large stockpot over high heat and wilt. Pour into a colander to drain and cool, and then squeeze all of the liquid from it and chop.
5
Combine the eggs, half-and-half, salt, and pepper in a medium bowl and whisk together.
6
Roll out the dough on a floured surface and fit into an 11-inch tart pan with a removable bottom. Spread the chopped Swiss chard on the bottom, and then layer with the cubed ham, the cheese, and most of the chopped green onions. Place the tart pan on a baking sheet and pour the egg mixture over the top, making sure to cover everything evenly. Top with the remaining green onions.
7
Bake until a toothpick inserted into the center comes out clean, about an hour. Let stand for 10 minutes before slicing and serving.
