Preheat oven to 350.
In a large bowl, combine flour, sugar, oats, cinnamon and salt and mix until combined. Set aside
Heat a small saucepan over medium heat. Add the butter and stir continuously until it melts. It may bubble a little. As soon as you see small brown specks in the butter, remove it from the heat. This took me about 3 minutes. Add the butter, along with the vanilla, to the oat mixture. Stir until moistened. This may take a minute or two! Fold in the peaches.
Butter and flour an 8×8 baking pan. Press batter into the pan. Bake for 25-30 minutes (the juicer your peaches are the longer you have to bake), the let cool completely – this can take up to 45 minutes! Cut and serve. Can be kept in the fridge or at room temperature in a sealed container.