Make the tart dough: Combine flour and salt in a medium bowl. Using your hands or a pastry cutter, break down the chilled butter in the flour until the butter resembles pea-size pieces. Add ice water and use a fork to combine. Use your hands to bring it together into one mostly uniform ball of dough, but be sure to not overwork it, to prevent the gluten from developing. Cut dough into two pieces, wrap in plastic, and put the dough in the refrigerator to chill for at least 1 hour. Place the second disc of dough in the freezer if you don’t plan to use it right away.
Make the filling and assemble the tart: Preheat oven to 375°F.
Wash and slice the escarole into 2-inch pieces. Heat a large sauté pan over medium heat with the olive oil. Once the oil is shimmering, add onion and cook until tender, about 5 minutes. Add garlic and cook until softened, about 1 minute. Stir in anchovies, breaking up the pieces with a spatula. Once the anchovy is incorporated, add escarole and stir until starting to wilt. Let the escarole cook down with the onions until very tender. Remove from the pan and set aside to cool.
While the escarole is cooling, prepare the currants. Heat up Scribe verjus in a small pot over low heat. (If you don’t have verjus, you can substitute equal parts red wine vinegar and water.) Add currants to the warm verjus and rehydrate for 5 minutes. Strain the currants and discard the liquid.
In a medium bowl, mix together the cooled escarole mixture, chopped capers, sliced olives, and pine nuts.
Roll out one portion of Tart Dough into a 12-inch circle. Spread the filling onto the dough, leaving a 2-inch border. Fold the border up over the filling to create the crust. Brush the crust with the beaten egg and bake 45 minutes.