Arrange the potato slices in an 8x8 baking dish. Season liberally with cumin spice sea salt and set aside.
Heat the olive oil in a large sauté skillet. Add the onions and garlic and cook until soft.
Deglaze the pan by adding the cold bourbon and allow to cook-off. Add the half & half and coffee rub and cook until hot and bubbly, about 5 minutes. Pour the hot mixture over the potatoes and set aside.
Make the crumble by combining all of the crumble ingredients and stirring together with a fork.
Scatter the crumble atop the potatoes and transfer to the oven.
Bake until the potatoes are cooked throughout, 40-45 minutes.