Simmer milk in a saucepan.

Mix egg, flour, and 1/2 cup sugar in an electric mixer bowl.

Beat mixture while pouring in the hot milk.

Pour sauce into a saucepan and beat over moderate heat.

Cook until thickened and smooth.

Melt remaining 1/2 cup sugar in a nonstick skillet, stirring until light caramel color.

Add orange rind and blend constantly.

Remove from heat.

Add caramel-orange mixture to the sauce and blend.

Line a mixing bowl with a sieve, pour sauce through, pressing to extract flavor from orange rind.

Discard the rind.

Add 1 cup heavy cream and stir.

Let cool.

Pour mixture into ice cream maker and freeze.

For butterscotch sauce: melt 1 1/2 cups sugar in nonstick skillet to dark caramel.

Add corn syrup, stir to blend, and remove from heat.

Stir in butter to blend.

Stir in 2/3 cup cream and bourbon.

Spoon sauce over ice cream and serve.