If using an ice cream maker with a removable canister, be sure to freeze the canister at least one day before you plan to make ice cream. Also note that the ice cream mixture needs time to chill before churning (at least an hour), and the churned ice cream needs about 3 to 4 hours in the freezer for a firmer, scoopable consistency.
Make the ice cream:
Preheat a skillet or medium/large sauce pan over medium heat. Add butter, if using, and pecans. Stirring frequently, cook for about 5 minutes or until toasted and fragrant. Reduce heat if necessary so nuts don't burn. Transfer to a plate to cool.
Return pan to the stove and add 1 cup of milk and the rolled oats. Bring to a simmer and cook until soft, about 10 minutes. Immediately transfer to a bowl or plate to cool.
In a blender combine the remaining 2 cups of milk, cashews, and ½ cup of the toasted pecans. Blend on high until completely smooth, about 1 minute. Add the cooled oatmeal, vanilla, maple syrup, sugar, salt, and bourbon, if using. Blend again until smooth and oats are fully broken down. Taste and add another 1 to 2 tablespoons sugar, if desired. Refrigerate until cold, or transfer to a container and place in freezer for about 30 minutes to speed up the process.
Roughly chop the remaining ¾ cup toasted pecans, and set aside.
Churn the mixture according the instructions for your ice cream maker. After churning, the ice cream will be softer than a typical soft serve consistency. Fold in the chopped pecans. For a firmer, scoopable consistency, transfer ice cream to a freezer-safe container, cover, and freeze for 3 to 4 hours.
Around the 4 hour mark, and definitely once the ice cream has been in the freezer longer, it will be too hard to scoop right out of the freezer. It's important to let the ice cream soften at room temperature for about 15 minutes before serving.
Optional butter: Since this is "butter pecan" the option is there to include it for the added bit of flavor, but I usually dry-toast the pecans in a skillet and skip the butter. The ice cream tastes great either way, so it's totally up to you! Bourbon/alcohol:Since alcohol doesn't freeze, adding it to homemade ice cream recipes is a common trick to help keep the ice cream a bit softer straight from the freezer. Since my oat ice cream recipes don't contain added oils, gums, or lots of refined sugar like store-bought ones, a small amount of alcohol can help with texture, but feel free to omit it. The flavor of bourbon pairs nicely with maple and pecans, but you can also use a neutral spirit like vodka.Note, don't add more than 1.5 ounces of any spirit, or the ice cream may not freeze properly. Storage and Serving:Store ice cream in an airtight container in the freezer. It tastes best when consumed within 1 week.Always allow about 15 minutes for the ice cream to soften before serving.Nutrition facts are estimates. Calculations do not include the optional butter.