To make the crust, whisk together the flour, buttermilk powder, salt, and baking powder., Add the shortening, working it in till it's thoroughly dispersed throughout the dry ingredients., Cut the butter into pats, and roughly work it into the mixture in the bowl; a few large pieces remaining are OK., Sprinkle the vinegar into the bowl, then 3 tablespoons of the ice water. Mix quickly and gently, just until everything is thoroughly moistened., Gather the dough into your hand, and squeeze it. If it holds together nicely, it's ready. If not, add a bit more ice water, a teaspoon or so at a time, until it's cohesive., Shape the dough into a rough disk, and transfer it to a well-floured work surface. Roll it into a rectangle about 8" x 12". Fold the rectangle like a letter, turn it 90°, and roll it into an 8" x 12" rectangle again. Give it another three-fold, then fold it in half to make a thick square. Wrap in plastic, and refrigerate for 30 minutes, or for up to 24 hours., Remove the dough from the fridge, and allow it to warm for about 15 minutes before rolling. While it's warming, preheat the oven to 375°F. Roll the dough into a 12" to 13" circle., Transfer the crust to a 9" pie plate. Trim the edges (patching any bare spots, if necessary), and make a tall crimp., Refrigerate the crust while you make the filling. Note: You may choose to make the filling during the dough's initial chilling period, instead of once it's shaped. Doesn't matter; either way is fine., Beat the eggs, sugar, and salt for about 2 minutes at high speed, until they're thick and light-colored., Stir in the flour, the cooled, melted butter; the espresso powder, and the flavor of your choice, then the chocolate chips/chunks and the diced pecans., Pour the batter into the pie crust, then scatter the pecan halves on top., Bake the pie for 30 minutes. Tent it lightly with aluminum foil, and bake for an additional 15 minutes, till the crust and top are both golden brown., Remove the pie from the oven, and allow it to cool for about 30 minutes before serving. Top with ice cream or whipped cream, if desired.