Stir the wet ingredients. In a large bowl, combine the peanut butter, honey (or maple syrup), and vanilla.
Mix until smooth and glossy.
Add the dry ingredients. Stir in the oats, protein powder, chia or flax, and salt. The mixture will be thick and a bit crumbly at this stage.
Adjust texture. Add milk 1 tablespoon at a time and mix until the dough holds together when pressed. You want it soft but not sticky.
Fold in the extras. Add chocolate chips or cacao nibs and mix just to distribute evenly.
Chill briefly (optional but helpful). Pop the bowl in the fridge for 10–15 minutes.
Slight chilling makes rolling easier and cleaner.
Roll into balls. Scoop about 1–1.5 tablespoons of dough per ball and roll between your palms. You should get 18–22 balls, depending on size.
Set and store. Place on a lined tray and chill for 20–30 minutes to firm up. Then transfer to an airtight container.