Preheat oven to 350F.
Evenly scatter oats on a baking pan lined with parchment and bake until golden brown and fragrant -- anywhere from 5 to 10 minutes, depending on the oven.
Stir them around once in a while to prevent any burning. Any burnt oats will make your ice cream taste bitter.
Using the same tray you used for your oats, toast your walnuts for 5-7 minutes, stirring once or twice to prevent burning. Cool, chop roughly, and set aside.
Seed the vanilla bean. Save the pod for your milk and cream. Save the seeds for a project on another day. (I like to make vanilla sugar with my seeds. With your hands, rub the seeds into a huge amount of granulated sugar and keep on hand for baking. Perfect for vanilla crème brûlée, anglaise or plain vanilla ice cream!)
Combine the vanilla bean pod, a generous pinch of salt, homogenized milk, and heavy cream in a medium pot over medium-high heat. Once the mixture is hot, add your freshly toasted oats to the milk and let them steep 15-20 minutes over medium heat.
Taste the milk to ensure the oats have steeped good flavor into your ice cream base. Over a bowl, strain the milk and oat mixture with a strainer lined with cheesecloth (or a thin towel) or mesh netted strainer) and squeeze (channel your inner hulk) the milk and cream from the oats.
You may want to wait for the oats in the cheesecloth to cool before wringing it out. ;)
Re-measure the milk mixture to ensure you will have 3 3/4 cups of milk as the oats will soak up liquid. You're looking for 3 3/4 cups of total liquid -- the recipe is overcompensating for what the oats will absorb.
Top as needed with milk or cream. Put the milk mixture back on the burner to reheat.
Whisk the egg yolks and sugar together. Once the milk is hot, add about 1 cup of the steeped milk to the yolk and sugar mixture, while whisking vigorously. Repeat this step with 1 more cup of steeped milk. Return custard to the remaining milk in the stock pot and heat through just to eliminate any grit from the sugar, then cook until the mixture coats the back of a spoon.
Strain the ice cream through a strainer into a container that fits in your fridge.
Cover with lid or plastic wrap and chill for 3 hours, or until thoroughly cool. Pour base into ice cream maker and spin until gorgeous and thick.
Pour into storage canisters, folding in toasted walnuts as you go. Line the top of the canister with parchment paper and freeze through for at least 4 hours.