Roast the sweet potatoes: Preheat your oven to 200°C (180°C fan). Scrub the sweet potatoes clean, prick them all over with a fork, and place them directly on the middle oven rack. Roast for 40–50 minutes, until the skins look crinkled and a knife slides through the flesh with no resistance — the flesh should feel as soft as warm butter when you squeeze gently.

Cool and scoop: Remove the sweet potatoes from the oven and let them sit until they're cool enough to handle, about 10 minutes. When you peel off the skin, it should come away in large strips, revealing deep orange flesh that smells sweet and earthy. Scoop the flesh into a large mixing bowl — you should have about 350 g of cooked sweet potato.

Blend the base: Add the softened butter to the warm sweet potato and beat with your mixer on medium speed for 2 minutes. Watch for the colour to lighten from deep orange to a pale apricot shade, and the texture to become fluffy and airy, like a cloud. The mixture should look smooth with no visible chunks.

Add the sugars: Pour in both the caster and brown sugars, then beat for another 2 minutes. You'll hear the mixer labour slightly as the sugar dissolves, and the mixture will become glossy, almost like a thick cake batter. Scrape down the sides of the bowl halfway through.

Incorporate the eggs: Crack the eggs into the bowl one at a time, beating on low speed after each addition. The mixture will loosen up and become satiny smooth — you should see a slight sheen on the surface. Stop as soon as each egg is fully incorporated; overbeating at this stage can make the pie crack during baking.

Finish the filling: Add the evaporated milk, vanilla extract, cinnamon, nutmeg, ginger, and salt. Mix on low speed until everything is combined — about 30 seconds. The batter should be pourable but thick, like a milkshake, with a warm golden colour and a fragrance that fills your kitchen with autumn spices.

Assemble and bake: Place your unbaked pie crust on a baking tray (this catches any drips and helps the bottom brown evenly). Pour the filling into the crust — it should come almost to the rim. Bake at 180°C (160°C fan) for 45–50 minutes. You'll know it's done when the edges are puffed and set, the centre jiggles only slightly like a firm jelly, and a knife inserted 5 cm from the edge comes out clean. The top should be a deep, glossy bronze colour, and your kitchen will smell like a bakery.

Cool completely: Transfer the pie to a wire cooling rack and let it cool for at least 1 hour at room temperature. The filling will continue to set as it cools — resist the urge to slice it warm, or you'll end up with a soupy mess. Once fully cooled, the surface should feel firm and slightly springy to the touch.