-
Place a large frying pan over a low to medium-low heat. Add the 1.5 tbs of olive oil, onion and garlic and reduce heat to low. Season with salt and pepper and cook, stirring occasionally, for 15 to 20 minutes, until the onions are golden brown. It is important to slowly caramelise the onions for a sweet taste!
-
Remove the onions from the pan and return the pan to the heat. Add the baby spinach and cook until wilted. Remove the baby spinach from the pan and leave to cool.
-
Increase the heat to medium/high and return the pan to the stove. Add the remaining olive oil and place the mushrooms, top side down. Cook until lightly golden (about 5 minutes) before turning over and cooking for a further 5 minutes or until golden. Remove from the heat, and drain on paper towel (top side up) as they will release a lot of liquid as they cool. Transfer the onions, spinach and mushrooms to the refrigerator and cool completely.
-
Preheat the oven to 200 degrees Celsius (400 Fahrenheit/gas mark 6).
-
On a lightly floured surface scattered with fresh thyme leaves, roll the pastry block out to the thickness of a £1 coin. Spread half the caramelised onions over the middle third of the pastry, making sure to leave an extra 2cm (3/4 inch) border at the edge of the pastry. Top with half of the baby spinach. Spread the dijon mustard over the mushrooms and season well with salt and pepper. Place the mushrooms on top of the spinach. Top the mushrooms with thyme and the remaining baby spinach and onions
-
Carefully roll the pastry over the top of the mushroom mixture until you have a log. Press down to seal the edges. Roll over the log so that the seam is facing the bottom.
-
Beat the egg and brush over the pastry. Then score the pastry with a knife - a herringbone shape looks nice!
-
Place the pastry on a baking sheet and tray and place in the oven for 30 to 35 minutes, or until golden and flakey. Serve warm.