Put the oats and 1 tablespoon of butter in a pan over low heat.
Toast these, stirring constantly, until they smell nutty.
Remove the oats from the heat.
In a separate pan on medium low heat, add 2 tablespoons of butter, brown sugar, and salt. Let it cook, stirring frequently until the brown sugar has melted a bit and it looks smooth.
Add the oats we just toasted to the brown sugar/butter mixture, and stir until all the oats are coated.
Keep stirring this (I like to use a heatproof spatula so the mixture doesn't stick to the bottom of the pan) until the brown sugar mixture starts to clump up on the oats
Remove the oat/brown sugar mixture from the heat and it will start to get crispier as it cools.