Preheat the oven to 325°F (163°C). Spread the Lucky Charms cereal without the marshmallows on a rimmed baking sheet and toast for about 8 minutes until fragrant. Allow the cereal to cool slightly.
1½ cups (55 g) Lucky Charms cereal
Place the Lucky Charms marshmallows in the freezer for about 30 minutes before churning the ice cream.
In a large bowl combine the heavy cream, whole milk, and buttermilk. Add the toasted cereal and allow it to soak for about 15 minutes, stirring once or twice so the cereal softens evenly.
1½ cups (360 ml) heavy cream, 1½ cups (360 ml) whole milk, ½ cup (120 ml) buttermilk
Transfer the soaked cereal mixture to a blender or food processor and blend until the cereal is broken down into very small pieces and the mixture appears slightly frothy.
Pour the blended mixture through a fine mesh strainer into a medium saucepan, pressing gently with a spoon to extract as much cereal milk as possible. Discard the remaining cereal solids.
Add the granulated sugar, milk powder, corn syrup, and kosher salt to the saucepan. Heat over low heat, stirring constantly, until the mixture is warm and small bubbles begin forming around the edges.
½ cup (100 g) granulated sugar, 2 tbsps (14 g) nonfat dry milk powder, 1 tbsp (20 g) light corn syrup, ¼ tsp (1.5 g) kosher salt
Place the egg yolks in a mixing bowl. Slowly whisk in about ¼ cup (60 ml) of the warm milk mixture. Repeat with another ¼ cup (60 ml) to gradually bring the eggs up to temperature.
4 large (72 g) egg yolks
Pour the tempered egg mixture back into the saucepan and cook over low heat, stirring constantly, until the custard thickens enough to coat the back of a spoon. Do not allow the mixture to boil.
Pour the cooked custard through a fine mesh strainer into a clean bowl to make sure you have a completely smooth base. Stir in the vanilla extract.
1 tsp (5 ml) vanilla extract
Place the bowl in an ice bath and stir until the custard cools to room temperature. Transfer to the refrigerator and chill until completely cold, preferably overnight.
Churn the chilled base in an ice cream maker according to the manufacturer’s instructions. During the final minute of churning add the frozen Lucky Charms marshmallows and allow them to mix in evenly.
1 cup (25 g) Lucky Charms
Transfer the ice cream to a freezer-safe container and freeze until firm, about 4 hours.