Preparation Preheat oven to 450°F. Unfold crust in 9-inch-diameter tart pan with removable bottom. Press crust onto bottom and up sides of pan. Fold overhang in and press, forming high-standing rim 1/2 inch above pan sides. Pierce all over with fork. Bake crust until set and pale golden, about 10 minutes. Cool in pan on rack. Reduce oven temperature to 350°F. Grate peel from 2 oranges (orange part only); place in small saucepan. Cut pith from oranges; discard. Working over same pan, cut between membranes to release orange segments into pan. Add 1/4 cup sugar, 1/4 cup water and lemon juice. Bring to boil. Reduce heat; simmer until mixture is thickened and segments have fallen apart, stirring often, about 22 minutes. Cool to room temperature. Mix cornstarch and 1 cup sugar in medium bowl. Beat in butter. Add egg; beat until fluffy. Stir in orange mixture and Grand Marnier (mixture will look curdled). Spoon into crust. Bake tart until set, about 45 minutes. Cool on rack. (Can be made 1 day ahead. Cover; chill.) Garnish with orange slices. Serve cold or at room temperature.
Preparation Preheat oven to 450°F. Unfold crust in 9-inch-diameter tart pan with removable bottom. Press crust onto bottom and up sides of pan. Fold overhang in and press, forming high-standing rim 1/2 inch above pan sides. Pierce all over with fork. Bake crust until set and pale golden, about 10 minutes. Cool in pan on rack. Reduce oven temperature to 350°F. Grate peel from 2 oranges (orange part only); place in small saucepan. Cut pith from oranges; discard. Working over same pan, cut between membranes to release orange segments into pan. Add 1/4 cup sugar, 1/4 cup water and lemon juice. Bring to boil. Reduce heat; simmer until mixture is thickened and segments have fallen apart, stirring often, about 22 minutes. Cool to room temperature. Mix cornstarch and 1 cup sugar in medium bowl. Beat in butter. Add egg; beat until fluffy. Stir in orange mixture and Grand Marnier (mixture will look curdled). Spoon into crust. Bake tart until set, about 45 minutes. Cool on rack. (Can be made 1 day ahead. Cover; chill.) Garnish with orange slices. Serve cold or at room temperature.