Frozen Yogurt

Ingredients
1-1/2 cups low fat milk
1 cup plain yogurt, store-bought or homemade
2/3 cups sugar
1 tablespoon cornstarch
1-1/2 teaspoons vanilla extract
Optional stir-ins: fruit, chocolate, cookies, etc. (I used frozen raspberries, thawed and mashed.)
In a heavy pot, combine sugar and cornstarch (leave out if using strained/Greek yogurt).  Stir in milk. Cook, stirring constantly, until mixture is thickened. Don't worry if mixture doesn't thicken without cornstarch. 

Remove from heat and cool.  Blend in vanilla and yogurt.  Freeze in your ice cream maker about half an hour or until it reaches soft serve consistency. If you want to add something smooth (melted chocolate, pureed fruit, etc.) you can add it now. If it is chunky, add it when ice cream is almost set.