In a bowl, let the beans soak in the buttermilk for a few minutes, then drain in a sieve. Place the sieve over a bowl.
Heat 3/4 cup olive oil and the chili oil in a 10-inch skillet over high heat. While the oil is heating, sprinkle the coating over the beans and shake in the sieve to coat the beans well. Repeat with the coating that falls into the bowl. Don't worry if they don't absorb all the coating.
Carefully add the beans to the hot oil, spread them into an even layer, and cook without stirring until they are browned and crisp on the bottom, 6 to 7 minutes. Turn with a spatula and brown on the other side, another 5 to 6 minutes, adjusting the heat so they don't burn. When they are evenly browned, add sliced garlic and brown for another 3 minutes. Season with salt and pepper, to taste. Add chiles to the pan, and continue to fry for another 15 seconds before adding the sage. With a slotted spoon, transfer the beans to paper towels to drain. Saute until the leaves turn crisp, about 1 minute. Top with lemon zest, then remove from the heat.
The Arborio Rice Coating is by far the best coating I know for anything fried. It gives an especially crisp crust to fried fish fillets, squid, shrimp, eggplant and veal cutlets. You may as well make a lot because it keeps well in the freezer, and it's hard to grind less than 1 cup of rice in a blender. If you have a spice mill, you can halve the recipe.
Arborio Rice Coating is one of the few places I use table salt. Sea salt and kosher salt are too heavy to stay evenly distributed in the coating.
Bringing the beans up to a simmer slowly helps keep the skins from splitting.
Arborio Rice Coating:
1 cup Arborio rice
3 cups all-purpose flour
1 cup semolina
2 tablespoons table salt
1 teaspoon freshly ground black pepper
Grind the rice in a blender until very fine. Put it in a bowl and add the all-purpose flour, semolina, salt and pepper. Toss until well blended. Store in a sealed container in the freezer for maximum freshness.