Preheat the oven to 350 °F. Line two large cookie sheets with silicone mat.
Cream together butter and sugar in a bowl. Add the egg, molasses and vanilla and mix until well combined. Add the baking soda, cinnamon, nutmeg and salt and combine. Mix in the oats and oat flour until fully incorporated. Fold in your add ins.
Scoop 1.5-2 tablespoon of dough and place on your prepared baking sheet.
Bake for 8-11 minutes until the edges are set and very lightly browned. The centres will be soft.
Let cool on the baking sheet for 10 minutes before using a spatula to move cookies to a wire rack to cool completely.