Heat a little olive oil in a large nonstick saute pan. Add the onions and 1 cup of the mushrooms and saute over a medium heat. If they are frozen, they will release a lot of liquid so just keep cooking, stirring regularly, until all the liquid has evaporated from the pan.
olive oil or butter, 1 cup diced onion, 4 cups sliced mushrooms
Now add the garlic and the remaining mushrooms 1 cup at a time, each time sauteeing until the liquid evaporates before adding the next cup.
1 tbsp minced garlic
Add the broccoli and sweet potato and mix through until they are mostly defrosted.
2 cups broccoli florets, 1 cups cubed sweet potato
Add the peas, corn or mixed veggies, the herbs and the flour. Mix through until the flour is coating the veggies and the herbs are fragrant.
1 cup frozen peas, corn or mixed vegetables, 2 tbsp provencal herb mix, 2 tbsp flour
Add the beans, wine and broth. Bring to a gentle simmer, just for a few minutes until the liquid has thickened and the wine has burnt off a little.
14 oz can of white beans, 1/2 cup white wine, 1 cup meatless chicken style broth
Remove from the heat. Add the cream, mustard and cheese and stir through until the creamy sauce has formed.
1/2 cup heavy (double) cream, 1 tbsp dijon mustard, 2 cups grated cheddar cheese
Lay a sheet of pastry over the bottom of your pie dish. Cut to size, allowing a little overhang on the sides, and scoop in the filling.
2 rolls pie crust (shortcrust pastry)
Add another layer of pastry over the top and cut to size. Press the edges of both the top and bottom crust together. Slightly roll them in, then gently press with a fork all around the edge to seal and score it. Use a fork or knife to poke a few holes through the top of the crust too - this will allow steam to escape while it cooks.If you wish, you can use the offcuts of pastry to make shapes to add to the top. Whisk an egg white or yolk in a small dish, and brush it all over the top of the crust.
1 egg white or yolk
Bake at 180C (360F) for 35-45 minutes, until the crust is golden. Allow to sit for about 5 minutes before cutting in.