Bring milk and cream to a boil in a medium saucepan over moderate heat. Remove from heat and whisk in 1 cup dulche de leche until dissolved.
Whisk in vanilla extract and let the mixture cool completely. Chill for at least 4 hours or overnight.
Freeze in ice cream machine until it is almost firm. Fold in the pecans, if using. Transfer ⅓ of the ice cream into a freezer safe ice cream container, swirl a few tablespoons of the reserved dulce de leche, followed by ⅓ of the ice cream and another layer of dulce de leche. Repeat until all of the ice cream and dulce de leche are used up. Freeze.
View the recipe instructions at Cook's Hideout
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