Preheat the oven to 375 degrees F.
In a large bowl, combine the peaches, liqueur, nutmeg, brown sugar, granulated sugar and corn starch. Mix together. Pour mixture into a 13-inch-by-9-inch casserole dish
Combine the flour, sugar, salt, and baking powder in a large bowl and mix. Cut in the butter with a fork until the dough resembles sand. Slowly add the buttermilk until the dough comes together. You may not need all of the buttermilk.
Place the dough on a floured surface and knead it into a 13-inch-by-9-inch rectangle about 1/2-inch thick and place over the peach filling. Use egg white as a wash, brushing on top of dough. Sprinkle the 11/2-tablespoons of sugar on top. Cook the cobbler until the top is golden brown, about 40 minutes.