Prepare Oven and Baking Surface: Preheat your oven to 375°F (190°C) and position a rack in the center. Line a large baking tray with parchment paper to prevent sticking and make cleanup easier.
Grind the Sichuan Peppercorns: Place the Sichuan peppercorns into a spice grinder and pulse until they turn into a coarse powder. This releases their unique numbing aroma and flavor, essential for the mala chili oil.
Combine Spices and Aromatics: In an oven-safe bowl or heat-resistant ceramic dish, mix the ground Sichuan peppercorns, red pepper flakes, gochugaru (if using), minced garlic, and kosher salt. This blend will form the flavorful base of your chili oil.
Heat the Oil: Pour the vegetable oil into a small saucepan and warm it over medium heat for 3 to 4 minutes, aiming for a temperature around 325°F (160°C). The oil should be hot but not smoking.
Infuse the Chili Oil: Carefully pour the heated oil over the spice and garlic mixture. The hot oil will bubble and sizzle, intensifying the flavors. Let this sit while you roast the edamame, allowing the oil to infuse thoroughly.
Toss Edamame with Oil and Salt: In a mixing bowl, coat the edamame pods evenly with the vegetable oil and kosher salt. Spread them out in a single layer on the prepared baking sheet.
Roast the Edamame: Place the tray in the oven and roast for about 20 minutes. At 15 minutes, check the color of the edamame pods—if lightly golden on the bottom, continue roasting for 5 more minutes; if still pale, extend roasting by 8 to 10 minutes. The goal is a golden, slightly crisp exterior.
Combine and Serve: Remove the edamame from the oven and immediately drizzle the infused chili oil over the pods, making sure to scoop up the flavorful garlic and pepper sediment as well. Toss gently to coat all pods thoroughly. Serve right away for the best texture and flavor.