Preheat your oven to 200°C (400°F) and line a large shallow roasting pan with your vegetables. Toss the broccoli florets and chopped onion with 2 tablespoons of olive oil, a generous pinch of sea salt, and several cracks of black pepper. Spread everything in a single layer—don't crowd the pan. This matters because crowding creates steam instead of caramelization. Slide it into the oven for exactly 10 minutes. Your vegetables should just start softening at the edges.

Remove the roasting pan and stir in your gnocchi plus the remaining 1 tablespoon of olive oil. Toss everything together so the gnocchi gets coated with the pan's cooking juices. Return to the oven for another 10 minutes. Don't worry if the gnocchi sticks slightly to the bottom—that's actually creating texture and flavor. While this is roasting, make your sauce (see Step 3).

In a medium bowl, mix the cornstarch with just 3-4 tablespoons of cold milk until completely smooth—no lumps. This paste prevents lumps from forming when you add the rest of the liquid. Whisk in the crème fraîche until smooth and silky. Add the remaining milk in a slow stream while whisking constantly. Once combined, stir in two-thirds of the grated parmesan, the wholegrain mustard, garlic granules, and another pinch of salt and pepper. Your sauce should be smooth, slightly thick, and smell absolutely incredible—that garlic and mustard combination is sophisticated without being obvious.

When the gnocchi comes out of the oven, pour the creamy sauce directly over the top and stir gently to distribute evenly. Make sure the sauce reaches all the edges of the pan. Sprinkle the remaining parmesan cheese in an even layer across the top. Slide the whole thing back into the oven for a final 10 minutes, until the top is golden and the sauce is bubbling gently at the edges. Let it cool for 2 minutes before serving. This helps the sauce set slightly and prevents mouth-burning accidents.