The sweet tang of roasted summer peaches is the perfect complement to nutty pecan shortbread.
Preheat oven to 300 degrees. Butter a 5-by-9-inch loaf pan. Place 8 tablespoons butter, 1/4 cup brown sugar, and the granulated sugar in an electric mixer. Beat until light and creamy, about 4 minutes. Add flour, pecans, salt, and 1/2 teaspoon vanilla; beat for 5 minutes. Transfer dough to prepared pan, and spread evenly. Score dough into four bars, and prick the surface decoratively with a fork.
Bake until shortbread looks dry, about 1 hour. Transfer pan to a wire rack to cool. Increase oven temperature to 375 degrees.
Meanwhile, place remaining 2 tablespoons butter, remaining 1/2 cup brown sugar, and 3 tablespoons water in a 9-by-13-inch glass baking dish. Place in oven until sugar is dissolved, about 6 minutes. Remove from oven; whisk in remaining 1/2 teaspoon vanilla and liqueur. Place peaches in dish, cut side down; bake until tender, about 15 minutes. Cool in pan on a wire rack. Slip off peach skins. Turn shortbread out of pan, cut along the scored lines, and serve with the peaches.