Step 1

Trim the ends of the leeks. Halve crossways, then cut each piece in half lengthways. Wash well under cold running water.

Step 2

Heat the butter and oil in a frying pan over medium heat. Add the leek and cook for 5 minutes each side, turning carefully to prevent breaking.

Step 3

Add the vinegar and sugar, and simmer for 6 minutes or until the leek is golden and sauce thickens. Remove leek from the pan. Reserve the sauce.

Step 4

Preheat oven to 220°C. Line 2 baking trays with non-stick baking paper. Cut the pastry in half to make 2 rectangles. Spread ricotta over each rectangle, leaving a 1.5cm border. Arrange the leeks crossways over the ricotta. Bake in oven for 15 minutes or until the pastry is puffed and golden.

Step 5

Drizzle sauce over tarts. Sprinkle with lemon thyme leaves to serve.