Toast sesame seeds in a large cast-iron skillet over medium-high heat, stirring constantly, until fragrant and lightly browned (about 4 minutes).

Remove from heat and transfer to a bowl to cool slightly.

Pulse oatmeal in a food processor until powdery.

Add toasted sesame seeds to the food processor and pulse until coarsely ground, leaving some whole seeds for texture.

Transfer the sesame-oatmeal mixture to a large bowl.

Add whole wheat pastry flour, unbleached white flour, buckwheat flour, stone-ground yellow or white cornmeal, sugar, and buttermilk powder to the bowl.

Stir thoroughly to combine all dry ingredients.

Sift baking powder, baking soda, and salt over the flour mixture a little at a time, stirring periodically to ensure even distribution.

Transfer the pancake mix into gallon-size zip-top freezer bags.

Label and date each bag.

Store bags of mix in the freezer to prevent rancidity.

Use the mix as needed, straight from the freezer.