Mushrooms with garlic and butter

1 kg mushrooms
1 onion, finely chopped
4 cloves garlic, crushed
1 tablespoon olive oil
1 tablespoon butter
pinch salt
pinch pepper
1/2 cup vegetable stock

Wipe and roughly chop mushrooms. Heat butter and oil in a large saucepan. Add garlic and onions to oil and cook over medium heat until soft but not brown. Add mushrooms and cover. Cook over low heat for a further 8-10 minutes or until mushrooms have softened. Blend together until desired consistency. If necessary add vegetable or chicken stock to create desired consistency. Serve warm or at room temperature.