While the mushrooms soak, prepare the dressing. Place the minced garlic in a heatproof bowl. Heat the neutral oil in a small pot until it starts to form tiny bubbles, then carefully pour it over the garlic to release its aroma. Stir in the chili flakes, ground Sichuan pepper (if using), sugar, soy sauce, black vinegar, and sesame oil. Mix well, adjusting the flavors to suit your taste.