Heat a splash of vegetable oil, and fry the mince until brown and crumbly. This will take about 10 minutes. Drain, and set aside.
In the same pan, heat another splash of oil, and fry the diced vegetables and garlic for 10 minutes. Return the mince to the pan, and add the flour. Stir through, and add the beef stock, ale, worcestershire sauce, tomato puree, and curry powder. Simmer for 30 minutes. Transfer to a pie dish, and refrigerate for one hour.
To make the pickled onions, place the sliced onion in a bowl, season with salt, and add the white wine vinegar. Leave to pickle until the cottage pie is ready.
Boil the potatoes in a large pan of salted water for about 15 minutes. Drain, and add the butter, milk and Dijon mustard. Mash until smooth.
Pre heat the over to 200 C / 390 F. Take the pie dish out of the fridge, and spread the mashed potato over the top and make peaks with a fork. Sprinkle with the blue cheese. Cook in the oven for 20 minutes.
Cook the frozen peas for the time specified on the packet. Once the cottage pie is cooked, grill for 2 minutes to crisp up the potatoes. Serve with pickled onions, and peas.