Make the crust: In a large mixing bowl, whisk the flours, Stevia In The Raw®, Sugar In The Raw® Organic White, and salt. Using a box grater, grate the frozen butter over the mixture. Gently rub the butter into the flour to incorporate. Set aside.
In a medium mixing bowl, stir to combine the buttermilk, vinegar, and ice. Pour half of the wet mixture over the dry mixture and gently toss to combine. Incorporate more of the wet mixture and gently knead until the dough just comes together into a shaggy mass. Divide in half, flatten into discs, wrap in plastic wrap, and chill at least 1 hour or overnight.
Lightly flour a work surface and place half of the chilled dough on it. Lightly flour a rolling pin. Roll out dough, applying even pressure with the rolling pin, into a 14” circle. Loosely roll dough around rolling pin and transfer and secure into a 10” pie pan. Trim edges of dough to have a 1” overhang and chill in the refrigerator. Place second dough round on work surface and roll out as above. Cut dough into ten, 1 ½” strips. Place the strips on a sheet pan and chill in the refrigerator.
Make the filling: In a large mixing bowl, combine the strawberries and nectarines and sprinkle with 2 tablespoons of Stevia In The Raw® and Sugar In The Raw® Organic White. Stir gently to combine and allow the fruit to macerate at room temperature for 20 minutes. Drain the fruit mixture of excess liquid and add the grated apple and lemon juice. Set aside.
In a small mixing bowl, combine ½ cup of Stevia In The Raw®, ½ cup of Sugar In The Raw® Organic White, flour, and salt. Gently fold the dry mixture into the fruit mixture. Pour into chilled pie shell. To arrange lattice crust over the filling, place dough strips 1/2” apart on the pie, weaving remaining dough strips through them in a basket-weave pattern. Trim lattice edges to meet the overhanging dough of bottom crust. Cut or crimp edges. Chill the pie in the refrigerator for at least 15 minutes to set the pastry.
Preheat oven to 425° F. Line a large rimmed baking sheet with parchment paper.
Remove the pie from refrigerator and brush lattice with egg wash and sprinkle with 1 tablespoon of Stevia In The Raw® and 1 tablespoon of Sugar In The Raw® Organic White Place the pie on the prepared baking sheet and bake 30 minutes, then reduce oven temperature to 375° F and bake 40 to 50 minutes more, or until browned and bubbly. If the crust begins to get too dark, cover with foil and continue a few minutes longer. Remove to a rack and cool at least 1 hour.