Best Ever Mushroom Sauce | Australian Mushrooms

Ingredients

• 30 g butter
• 2 tbsp olive oil
• 1 large brown onion, finely chopped
• 200 g cup mushrooms, trimmed, quartered
• 200 g Swiss brown mushrooms, trimmed, quartered
• 2 tbsp plain flour
• 1 ½ cups beef stock
• ⅔ cup thickened cream
• 1 tsp Dijon mustard
• 2 tbsp chopped flat-leaf parsley