Add the heavy cream, whole milk, brown sugar, and maple syrup to a large saucepan over medium heat. Cook, stirring frequently, until the sugar is dissolved, about 5 minutes.

In a bowl, whisk together the eggs, vanilla, cinnamon, and salt.

Slowly whisk in about ¾ cup of the hot cream mixture into the egg mixture. Make sure to keep whisking as you temper the eggs.

Pour the egg mixture into the saucepan with the cream. Cook, stirring constantly, until the custard reaches 170 to 175°F, about 5 to 7 minutes. Do not let it boil.

Strain through a fine mesh strainer into a bowl. Cover and refrigerate overnight.

Melt the butter in a skillet over medium heat. Add the apples, sugar, and cinnamon. Cook for 8 to 10 minutes, until the apples are tender. Transfer to a storage container and cool for 10 minutes. Toss with 1 tablespoon of the caramel and chill until cold.

Churn the base according to the manufacturer’s instructions. In the last 5 minutes, add the apples and walnuts. In the last 1 to 2 minutes, drizzle the caramel in slowly.

Serve as soft serve now, or freeze until firm. If frozen solid, let the container sit on the counter for 10 to 15 minutes before scooping.