Preheat oven to 200C (390F)
Add onion, garlic and 100g of white potato into the Thermomix bowl and chop with the measuring cup (MC) on for 4 seconds | Speed 5
Scrape down the sides of the bowl, add oil and sauté with the MC off for 3 minutes | Varoma | Speed 1
Add beef, season with salt and pepper and brown with the MC off for 5 minutes | 100C | Reverse | Speed 1
Add Worcestershire sauce, tomato paste, beef stock and carrots into the Thermomix bowl and close the lid
Add remaining white potato and sweet potato into the Varoma bowl, assemble the Varoma and place on top of the Thermomix
Cook for 20 minutes | Varoma | Reverse | Speed soft
Remove the Varoma, add peas into the sauce and stir with the spatula to combine
Pour meat sauce into a square roasting dish and rinse out the Thermomix bowl
Put the potatoes into the bowl, add milk and cook with the MC off for 9 minutes | 100C | Speed 1
Add salt, pepper, seeded mustard, add butterfly and mash for 20 seconds | Speed 3
Layer mashed potatoes on top of the beef filling, use a fork to rough up the top of the potatoes and sprinkle with the grated cheese
Bake in the oven on the middle shelf for 20-30 minutes or until the top is browned