Grease a 9" square baking pan with butter.
Dust the pan with flour and shake out the excess.
Preheat the oven to 350 ℉.
Melt the butter in a small, heavy-bottomed saucepan over low heat, stirring often. Remove the pan from the heat and let cool for 5 minutes. Stir in the vanilla.
In a large bowl, combine the oats, flour, sugar, salt and cinnamon with a wooden spoon, leveling out any lumps. Pour in the butter mixture and mix until well incorporated. Stir in the cherries (or other dried fruit) and continue mixing. Stir in the nuts if wanted.
Spread the dough evenly in the pan, using your clean fingers to pat down.
Bake for 30 minutes or until the top is golden and the edges are slightly pulling away from the sides of the pan.
Remove the pan from the oven and cool on a rack for at least 1 hour. Cut before serving within 3 days.