Infuse Milk and Cream with Vanilla: In a heavy-bottomed saucepan, gently warm the whole milk and heavy cream together. Split the vanilla bean pod lengthwise and scrape out the seeds using the back of a knife. Add both the seeds and the pod into the milk mixture. Heat the liquid over medium heat until it begins to simmer lightly, with tiny bubbles forming around the edges. Avoid boiling to prevent curdling. Once it reaches this stage, remove the pan from heat.
Whisk Egg Yolks and Sugar: In a medium-sized bowl, combine the egg yolks and granulated sugar. Whisk vigorously until the mixture becomes pale, thickened, and slightly fluffy, indicating the sugar has dissolved and the yolks have lightened.
Temper the Egg Yolks: Slowly pour a small amount of the warm milk mixture into the yolks while continuously whisking to gently raise their temperature. Gradually add the rest of the milk mixture in a slow, steady stream, whisking constantly to prevent the eggs from scrambling.
Cook the Custard Base: Transfer the combined mixture back into the saucepan. Place it over low heat and stir continuously with a whisk or wooden spoon. Cook gently until the custard thickens enough to coat the back of a spoon and holds a trail when you run your finger through it. Take care not to boil, as overheating can cause the eggs to curdle.
Strain and Toast Marshmallows: Remove the vanilla pod and pour the custard through a fine mesh sieve into a clean bowl to ensure a silky texture. Next, spread half of the mini marshmallows evenly on a baking sheet and place them under the broiler (grill) until they develop a golden brown, toasted surface. Watch closely to avoid burning.
Incorporate Toasted Marshmallows and Chill: While the custard is still warm, stir in the toasted marshmallows until they melt and fully blend into the custard, imparting a rich toasted flavor. Cover the bowl with plastic wrap, pressing it directly onto the custard’s surface to prevent a skin from forming. Allow the custard to cool to room temperature, then refrigerate for at least two hours, or ideally overnight, to chill thoroughly.
Churn the Ice Cream: Pour the chilled custard into your ice cream machine and churn according to the manufacturer’s instructions. The mixture will transform into a smooth, soft-serve consistency.
Add Final Toasted Marshmallows and Freeze: Toast the remaining mini marshmallows under the broiler as before. Gently fold them into the churned ice cream. Transfer the ice cream to a freezer-safe container and freeze for a minimum of six hours to firm up. When ready, scoop and serve your delicious homemade toasted marshmallow ice cream!