Step 1

Melt butter in a large frying pan over medium heat. Add onion and cook, stirring, for 5 to 7 minutes or until softened.

Step 2

Add garlic and sugar. Cook, stirring, for 2 minutes or until sugar is dissolved. Add vinegar and cook, stirring occasionally, for 5 minutes or until liquid is absorbed and onions are caramelised. Remove from heat.

Step 3

Preheat oven to 200°C. Line a 23cm loosebased fluted tart pan with pastry, trimming excess. Refrigerate for 30 minutes.

Step 4

Place pan on an oven tray. Cover pastry with baking paper. Fill with uncooked rice or ceramic pie weights. Bake for 10 minutes. Remove paper and rice or weights. Reduce oven temperature to 180°C.

Step 5

Spoon onion mixture over pastry. Whisk eggs and sour cream in a jug until well combined. Season with salt and pepper. Pour egg mixture over onion mixture. Sprinkle with ricotta and thyme. Bake for 25 to 30 minutes or until tart is golden and just set. Remove from oven. Set aside to cool for 5 minutes. Remove from pan.

Step 6

Cut into wedges.