1Heat the oil in a non-stick frying pan over high heat. Add the mushrooms and chopped rosemary. Cook for 5 minutes or until the mushrooms are tender. Set aside to cool for 10 minutes.
2Meanwhile, preheat oven to 200°C fan forced. Lightly grease three, 12 hole, 30ml-capacity mini muffin pans with olive oil spray.
3Sift the flour and baking powder into a bowl. Add the parmesan and season with salt and pepper. Using a fork, whisk the eggs and buttermilk together in a jug. Pour the egg mixture into the dry ingredients. Add the butter and stir until almost combined. Fold in the mushrooms.
4Spoon mixture into muffin holes until almost full. Bake for 18–20 minutes or until a skewer inserted into a muffin comes out clean. Stand muffins in pan for 5 minutes then turn out onto a wire rack.
5Cut rosemary sprigs into 3cm lengths. Top muffins with a piece of salmon and secure with a rosemary sprig. Serve.
Note: You can make the muffins to the end of step 4, up to 4 hours ahead. To warm, place muffins on a baking tray and reheat in an 180°C fan forced oven for 5–8 minutes.
Tip: A quick and easy way to dice mushrooms is to trim the stem flush with the mushroom cup. Turn the mushroom stem-side down on a chopping board so it sits flat. This makes it easy to dice or slice.