Place Brown Sugar (1 cup), Milk (2 tablespoon), Unsalted Butter (1 1/2 tablespoon), and Vanilla Extract (1 teaspoon) in a heavy saucepan over medium heat. Cook until the sugar is dissolved and butter is melted. Bring mixture to a boil, stirring constantly.
Add Pecans (3/4 cup) and continue to boil slowly for about 4 minutes. Remove from heat.
Drop pecan mixture by spoonfuls onto parchment paper - so that they form little rounds of pecan and melted sugar that spread out on the paper.
Cool the pralines completely before using, about 20-30 minutes.
Preheat oven to 400 degrees F (200 degrees C). Line two baking sheets with parchment paper and set aside. Peel, pit and prepare the Peach (1 1/2 cup).
Combine Cake Flour (5 cup), Granulated Sugar (1/2 cup), Baking Powder (2 teaspoon), Baking Soda (1/2 teaspoon), and Salt (1/2 teaspoon) in a large bowl.
Add the dry ingredients to the bowl of a large (7 cups or greater) food processor fitted with the metal blade to cut the Unsalted Butter (1 1/2 cup) into the dry ingredients.
Pulse 10-12 times and transfer to a large bowl to continue making the dough.
Roughly chop the cooled pralines.
Add the pralines to the flour mixture.
Add Buttermilk (1 1/4 cup) and mix until just combined and dough begins to stick together.
Add the peaches and fold the dough over the fruit several times until the peaches and pralines are evenly distributed throughout the dough. Be careful not to overwork the dough.
Divide the dough into two equal portions. Lightly flour a work surface and turn one portion of the dough out onto it. Flatten the dough with lightly floured hands and form a 1 1/2" thick disc. Transfer to a baking sheet, and repeat.
Use a long, thin, sharp knife to cut into eight equal portions.
Make an egg wash by beating the Egg (1) together with the Milk (2 tablespoon). Lightly brush the scones with egg wash.
Sprinkle each with one tablespoon of Demerara Sugar (2 tablespoon).
Bake 30-35 minutes or until golden brown and firm to the touch. Remove from the oven and serve immediately.