Preheat the oven to 220°C. Line a large baking tray with greaseproof paper and drizzle with 1 tbsp of the oil.
Add the cauliflower florets to a large bowl. Drizzle with the other tbsp of oil and toss a few times. Add the flour and toss until the florets are coated. Pour in the milk and toss again. Add the corn starch and toss until the cauliflower is evenly coated. Spread the coated cauliflower on to the lined baking tray, making sure the pieces are evenly spaced out with gaps in between.
Meanwhile combine the rice vinegar, sherry, soy sauce, sugar, and corn starch for the sauce in a medium-sized bowl. Stir to dissolve the sugar and corn starch.
Add the oil, peppercorns, and red chillies to a small saucepan and turn the heat to medium-low. Once it becomes fragrant, add the ginger and garlic. Cook until they are just starting to brown, another 1 to 2 minutes. Stir the sauce again to re-dissolve the corn starch completely and add it to the pan.
Raise the heat to medium-high and bring it to a boil. Boil until the sauce is just thickened. Remove from the heat and set aside.
After the cauliflower has baked for 10 minutes, add the shallots, peanuts, peppers, and spring onions. Put the tray back in the oven and cook for another 15 minutes, until the peppers are lightly cooked.
Remove from the oven and pour the sauce over the cauliflower. Gently toss to coat. Serve immediately over rice.