You will need
2 onions, peeled and sliced into half rings
2 T (30 ml) white vinegar
½ cup (125 ml) water
2 T (30 ml) balsamic vinegar
¼ cup (60 ml) soft brown sugar
1 t (5 ml) Ina Paarman’s Seasoned Sea Salt
500 g Ina’s sour cream pastry or store bought all-butter puff pastry
1 egg yolk
a pinch of salt
a pinch of sugar
sprigs of thyme
Egg wash: 1 egg yolk or whole egg beaten with a pinch of salt and a pinch of sugar.
Place the sliced onions in a saucepan. Add white vinegar and water. Boil open for 5 minutes while stirring now and again. Strain and discard vinegar water. To the same saucepan with the onions, add the balsamic vinegar, sugar and Seasoned Sea Salt. Simmer with lid on for ± 20 minutes until thick and jammy.
Adjust oven rack to middle position and preheat oven to 200°C. Roll out the pastry, on baking paper and cut into a rectangle 44 cm x 22 cm. If using bought pastry, join 2 sheets to form a rectangle of ± 44 cm x 22 cm.
Using a pizza wheel or small sharp knife, cut off a 1 cm wide pastry strip all round to build up the edges. Make an egg wash by beating the egg , salt and sugar together. Glue the edge strips down with a egg wash. Prick centre all over with a fork. Cover the centre with baking paper and weigh down the middle using ceramic baking beans or dried beans. Bake blind for 15 minutes. Remove the baking paper and beans. Spread the Mushroom Pesto over the pre-baked pastry center. Top with the caramelised onion mixture.
Squeeze Cheese Sauce over onion and carefully spread. Be sure not to go onto the outer edge. Position the mushrooms stem side up on tart. Season mushrooms with Garlic Pepper Seasoning and drizzle with olive oil. Brush the outer edge of pastry with egg wash to give it a glossy finish..Bake for ± 20 minutes.
Garnish with sprigs of thyme.