Line your baking pan with parchment paper, leaving overhang on the sides for easy removal.
In a mixing bowl, combine the rolled oats and chopped nuts if using, stirring to distribute evenly.
In a small saucepan over low heat, melt the butter with honey and brown sugar, stirring constantly until the mixture is smooth and fragrant, about 3-4 minutes.
Remove the saucepan from heat and stir in vanilla extract to enhance the aroma.
Pour the warm, sticky mixture over the oats and nuts, folding gently with a spatula until everything is coated and sticky.
Transfer the mixture to the prepared pan and press firmly with the back of a spatula or your fingers to create an even, compact layer.
Let the mixture rest at room temperature for at least 30 minutes to set, or refrigerate for 15-20 minutes for quicker firming.
Once set, lift the slab out of the pan using the parchment overhang and place it on a cutting board.
Use a sharp knife to cut the slab into even squares or rectangles, wiping the blade clean between cuts for neat edges.
Serve immediately or store in an airtight container at room temperature for up to 3 days, or refrigerate for longer freshness.
