Best Mushroom Gravy

Name: Best Mushroom Gravy
Prep time: 5 min
Cook time: 15 min
Total time: 20 min
Cuisine: British
Ingredients: 3 tbsp olive oil; 3 garlic cloves (crushed); 1 large red onion (sliced); 375 g chestnut mushrooms (sliced); 3 sprigs rosemary (chopped); Large handful fresh thyme (chopped); 500 ml veg stock; 1 1/2 tbsp tamari ((gluten-free soy sauce) (22.5ml)); 2 tbsp corn flour ((16g)); 1 tbsp cacao powder ((8g)); Salt & pepper