Use a sharp knife to split the vanilla pods lengthwise, then scrape out the tiny black seeds with the back of the knife, collecting them in a small bowl.
Combine the heavy cream, whole milk, and vanilla seeds in a saucepan, and heat over medium until just beginning to simmer, releasing a fragrant aroma—do not boil.
In a separate bowl, whisk the egg yolks together with the sugar and a pinch of salt until smooth and slightly pale.
Slowly pour some of the hot cream mixture into the egg yolks, whisking constantly to temper the eggs and prevent curdling.
Pour the tempered egg mixture back into the saucepan with the remaining cream, stirring constantly until the custard thickens slightly and coats the back of a spoon—about 5-7 minutes.
Remove the custard from heat and strain it through a fine-mesh sieve into a clean bowl to remove vanilla pod pieces and any cooked egg bits.
Stir in vanilla extract if using, then cover the bowl with plastic wrap and chill in the refrigerator for at least 4 hours, preferably overnight, until completely cold.
Once chilled, pour the custard into your ice cream maker and churn according to the manufacturer's instructions until it reaches a thick, creamy consistency.
Transfer the soft ice cream into a freezer-safe container, folding in toasted nuts or caramel swirl if desired, and freeze for at least 4 hours to firm up.
When ready to serve, let the ice cream sit at room temperature for 5 minutes to soften slightly, then scoop into bowls and enjoy the speckled, fragrant vanilla flavor.
