Spanish tortilla - Good Food Middle East

Ingredients

• 1 large white onion, sliced
• 4 tbsp olive oil
• 25g butter
• 400g waxy potatoes, peeled, quartered and finely sliced
• 6 garlic cloves
• 8 eggs, beaten
• handful flat-leaf parsley, chopped, plus extra to serve
• 1 baguette, sliced
• 4 vine tomatoes, peeled and coarsely grated (see tip)
• drizzle of olive oil