Cut cold butter into cubes. With mixer on low, add butter to flour and mix until crumbly. Mix water and vinegar together, then slowly add to mixer on low just until dough begins to come together. Shape dough into a ball and cover with plastic wrap; refrigerate for at least 1 hour or up to 1 day. Remove dough and let stand still wrapped in plastic for 15 minutes at room temperature before rolling out on a lightly floured surface. Shape into an 11" tart pan with a removable bottom.
In a large bowl, beat eggs together lightly, then add half and half, salt, pepper and nutmeg and mix well with a whisk.
Place tart pan on a foil lined baking sheet. Spread spinach, feta cheese, and pine nuts evenly over the bottom of the tart crust. Gently pour egg mixture on top, being careful not to overfill. Return tart to oven and bake until lightly golden on top and a toothpick comes out clean, about an hour. Let cool slightly before removing outer rim from tart pan and serving.
Recipe by Cooking With MicheleĀ® at https://cookingwithmichele.com/2011/05/tarts-for-a-wedding-shower/