Buckwheat honey has a robust color and flavor that is both deeply floral and richly caramelly – almost like molasses. It balances the tartness of the slowly simmered apples in the filling and adds a really unique flavor that will appeal to any honey lover.
Make the crust: Whisk the flour, sugar and salt in a medium bowl. Add the butter and work it into the flour with your fingers until it is in small bean-size pieces. Drizzle in 3 tablespoons ice water and the vinegar and stir to moisten. Gradually add up to 2 more tablespoons ice water until the dough holds together when squeezed. Transfer to a sheet of plastic wrap, gather into a disk and wrap tightly. Refrigerate for at least 2 hours or overnight.
Meanwhile, prepare the filling: Peel and chop the apples. Put half of the apples in a blender with 1 cup water and puree until smooth. Gradually add the remaining apples and blend until smooth, adding more water 1/4 cup at a time as needed.
Pour the apple mixture into a large nonstick skillet and bring to a simmer over medium heat. Reduce the heat to medium low and simmer, stirring, until very thick and reduced to about 1 1/2 cups, 1 hour 15 minutes to 1 1/2 hours. Let cool.
Preheat the oven to 400˚ F. Roll out the pie dough on a lightly floured surface into a 12-inch round. Ease into a 9-inch pie plate. Fold the overhanging dough under itself and crimp the edge. Prick the bottom and sides of the crust with a fork and refrigerate until firm, about 20 minutes. Line the crust with parchment paper or foil and fill with pie weights or dried beans. Bake until the edges of the crust are dry and lightly browned, 15 to 20 minutes. Carefully remove the weights and paper and continue to bake until the bottom of the crust is dry and just starting to brown, 10 to 15 minutes. Transfer to a rack to cool. Reduce the oven temperature to 350˚ F.
Return the apple mixture to the blender along with 1/2 cup honey and the sugar; puree until combined. Add 3/4 cup heavy cream, the eggs, vanilla and salt and pulse until just combined.
Pour the mixture into the crust and bake until the filling is puffed and dry to the touch, 1 hour to 1 hour 15 minutes (tent the crust with foil if it is getting too dark). Turn off the oven and let the pie sit inside with the door cracked open, 5 to 10 minutes. Transfer to a rack to cool completely.
Make the topping: Beat the remaining 3/4 cup heavy cream and 2 teaspoons honey in a large bowl with a mixer until medium peaks form, 2 to 3 minutes. Spread on the pie.