First brown your butter. Heat butter over medium high heat until it melts completely. Lower the heat to low and cook until it is a golden color and brown solids start to appear. Remove from heat and set aside.
Stir together flour, baking soda, cinnamon, and salt. Set aside.
In a large bowl, cream together the brown butter, white sugar, and brown sugar until smooth. Beat in the eggs and vanilla until thick and creamy.
Use a spatula to combine the wet ingredients with the dry ingredients from step 2.
Add the oats and cranberry raisins and stir until well incorporated.
Let the dough sit for 30 minutes in the fridge.
Preheat oven to 375 degrees F (190 degrees C).
Cover 2 baking sheets with parchment paper. Use a 3 (1.5 oz) tablespoon ice cream scoop to scoop cookie dough onto the baking sheets. Cookies should be 2-3 inches apart. Sprinkle flaky sea salt on each cookie (optional).
Bake for 11-13 minutes until they are golden brown along the edges.
Cool for 10 minutes before transferring to a wire rack. Cool for another 10 minutes on the wire rack before serving.