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1
Put a rack in middle of oven and preheat to 400F.
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2
Butter gratin dish (see above) and sprinkle with sugar, knocking off excess.
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3
Bring milk just to a simmer in a small saucepan.Remove from heat.
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4
Melt butter in a 2 to 3 quart saucepan over low heat.
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5
Stir in flour and cook, stirring, for 5 minutes to make roux.
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6
Remove pan from heat and add milk in a steady stream, whisking constantly, then add remaining 2/3 cup sugar, whisking vigorously.
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7
Cook mixture over low heat, whisking, until smooth, about 2 minutes.
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8
Remove pan from heat and add egg yolks one at a time, whisking after each addition until incorporated.
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9
Slowly whisk in Grand Marnier.
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10
Cover mixture with a buttered round of wax paper and cool to room temperature.
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11
Beat 8 whites with salt in a large bowl with an electric mixer at medium speed until frothy.
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12
Add cream of tarter, increase speed to high, and beat until whites form stiff peaks.
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13
Stir one quarter of whites into yolk mixture to lighten it, then gently but thoroughly fold mixture into remaining whites.
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14
Reserve 1 cup of mixture and transfer remainder to gratin dish.
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15
Mound reserved mixture in center.
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16
Bake souffle until puffed and golden, 25 to 30 minutes.
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17
Serve immediately.
