Prepare the Baking Dish:
Line an 8x8-inch baking dish with parchment paper, leaving a bit of overhang on the sides to lift the bars out easily once set.
Combine Dry Ingredients:
In a large mixing bowl, combine the rolled oats, protein powder, and chia or flaxseeds, if using. Stir until evenly mixed.
Add Wet Ingredients:
In a separate bowl, mix the nut butter and honey until smooth. Gradually add the milk and stir until you get a cohesive, slightly thick consistency.
Combine Wet and Dry Mixtures:
Pour the wet mixture into the bowl with the dry ingredients. Mix thoroughly until everything is evenly combined. If the mixture is too thick, add a splash more milk to make it easier to combine.
Add Extra Ingredients:
Fold in any extras, like mini chocolate chips or dried fruit, to add flavor and texture.
Press into Baking Dish:
Transfer the mixture to the prepared baking dish. Use a rubber spatula to press the mixture down firmly and evenly.
Chill the Bars:
Place the baking dish in the refrigerator for at least 1–2 hours to allow the bars to set.
Slice and Store:
Once set, lift the bars out of the dish using the parchment paper overhang and cut into 8–10 bars. Store in an airtight container in the fridge for up to one week.