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 (watch the video at the beginning of this post to see what it should look like).
Remove the oat/brown sugar mixture from the heat and it will start to get crispier as it cools.