In medium, heavy-bottomed saucepan over medium heat, bring soy milk to boil.
Add ginger, remove pan from heat, cover, and let steep 30 minutes.
Strain soy milk, discarding ginger, and set aside.
In large nonreactive bowl, whisk together egg yolks and 6 tablespoons of sugar. Whisk in flour until well combined.
Gradually add hot milk, whisking constantly to prevent curdling. Return yolk mixture to saucepan and set over medium heat. Cook, whisking constantly, until custard boils and thickens enough to coat back of a spoon, 2 to 3 minutes.
Transfer to large bowl, whisk in pumpkin purée, and set aside.
Using electric mixer with whisk attachment, beat egg whites until foamy and slightly opaque.
With mixer running, add remaining 6 tablespoons sugar, 1 tablespoon at a time, then beat until stiff but not dry. Fold 1/3 of egg whites into pumpkin mixture to lighten, then add mixture to remaining whites, folding in gently but thoroughly.
Spoon batter into souffle dish, filling almost to top, and lightly run finger around inside rim to create a "moat.".
Bake until the soufflé has risen well above rim and tops are golden brown, about 25 minutes. Serve immediately.