1 (12 ounce) package frozen lightly-sweetened red raspberries, partially thawed, or 3 cups fresh red raspberries
¾ cup sugar
1 envelope unflavored gelatin
4 cups whole milk
4 eggs, beaten
½ cup frozen orange juice concentrate, thawed
Partially thaw frozen strawberries and raspberries, if using. Mash berries slightly to break up; set aside.
In a large saucepan, combine sugar and gelatin. Stir in milk. Cook and stir over medium heat until mixture just starts to boil. Remove from heat. Whisk about 1 cup of the hot mixture into beaten eggs; return all to saucepan. Cook and stir for 1 to 2 minutes or until an instant-read thermometer registers 175°F and mixture coats the back of a clean metal spoon. Do not boil. Stir in strawberries, raspberries, and orange juice concentrate. Cover and chill for 4 to 24 hours. (Mixture will be very thick after chilling.)
Transfer the mixture to a 4- or 5-quart ice cream freezer; freeze according to the manufacturer's directions. If desired, ripen.
To make ahead: Prepare ice cream as directed through Step 3. Cover; chill for up to 24 hours. Or prepare as directed through Step 4; freeze for up to 1 week.