Instructions

1. For Cascabel Chile Oil - To make the chile oil, preheat the oven to 350 degrees F. Place the cascabel and guajillo chiles on a baking sheet and roast until the guajillos turn dark red, about 5 minutes; remove, but do not turn off the oven.
2. Meanwhile, bring a small pot of water to a boil. Transfer the chiles to a medium heatproof bowl and cover with boiling water; let sit until the chiles are soft, about 20 minutes.
3. Drain the chiles and place them in a blender along with the 1-1/2 cups oil and the garlic;blend until the oil becomes clear and red. Once it is fully cooled, the cascabel oil can be stored in an airtight container until ready to use.
4. For Salsa Macha - Preheat the oven to 350 degrees F. Add the sunflower seeds and chiles to a small baking sheet. Roast for 2 minutes, then remove the chiles (leave the sunflower seeds on the pan); continue to roast the seeds until lightly toasted, about 5 minutes more.
5. Transfer the chiles to a medium heatproof bowl and add boiling water to cover; let soak until softened, about 20 minutes. Transfer the chiles (reserve the soaking water) to a blender; puree until a thick paste forms, adding a little of the soaking water only as needed to help blend. Add the toasted sunflower seeds, vinegar, garlic, and oregano; with the motor running, slowly drizzle in the oil until the salsa is emulsified but still lightly chunky. Taste and adjust the seasoning as necessary.
6. For Quesadillas - To make the filling, in a large skillet, heat the 1/4 cup oil over high heat. Add the onions and lower the heat to medium-high; cook, stirring occasionally, until softened and lightly browned in places, 5 to 6 minutes. Add the Brussels sprouts and season with salt; let cook, stirring occasionally, until the size of the leaves is reduced by half and their edges are beginning to brown, 5 to 7 minutes. Drizzle with 2 to 4 tablespoons of the chile oil to taste, and season with more salt as needed.
7. Preheat a large skillet or griddle to medium-high heat. Add all of the homemade or half of the store-bought tortillas, working in batches as needed to fit. Sprinkle the shredded cheese over one side of the homemade tortillas or across the full diameter of the store-bought ones. Quickly divide the Brussels sprouts mixture over the top (about 1/3 cup per quesadilla). Fold the homemade tortillas in half to cover; top store-bought tortillas with another whole tortilla to cover. Cook, flipping the quesadilla 1 to 2 times with a spatula, until the cheese is fully melted, 5 to 7 minutes total. Repeat with the remaining quesadillas as needed.
8. Transfer the quesadillas to four plates and garnish with the queso fresco and cilantro. Serve with the Salsa Macha.