Start by dropping your raisins into a small bowl of warm water, or better still a splash of grappa if you have it, and let them plump up for fifteen minutes while you get everything else ready. Meanwhile, tip the chestnut flour into a dry skillet over low heat and toast it gently for two or three minutes, stirring often, just until it smells warm and faintly sweet, almost like roasted chestnuts themselves. This little step is not traditional in every valley kitchen, but my nonna swore by it, saying raw chestnut flour can taste flat and slightly bitter, while toasting coaxes out its natural sweetness. Do not let it darken or scorch, you only want to wake it up, not cook it through. Set it aside to cool for a few minutes before it meets any liquid.

In a large bowl, combine the toasted chestnut flour with the pinch of salt, then begin pouring in the cold milk and water in a slow, steady stream while whisking constantly. Chestnut flour has no gluten to speak of, so it clumps stubbornly if you dump the liquid in all at once, and there is nothing sadder than biting into a dry pocket of raw flour in an otherwise silky cake. Work patiently, adding the liquid in three or four additions and whisking out every lump before adding more. Once smooth, whisk in the melted butter and olive oil until the batter turns a deep, glossy brown, almost like liquid chocolate. If you are using honey or sugar, stir it in now so it dissolves fully.

Cover the bowl with a clean kitchen towel and let the batter sit undisturbed for twenty minutes at room temperature. This resting time matters more than it looks like it should, because chestnut flour is thirsty and needs time to fully absorb the milk and water, which is what gives the finished cake its characteristically dense, almost pudding-like crumb rather than a gritty one. While you wait, drain your raisins well and pat them dry with a cloth, and preheat your oven to 180°C (350°F). Use this pause to get your pan ready too, since a rested batter should go into the oven without much more delay.

Generously butter a 22 to 24cm (9-inch) round cake or springform pan, then dust it lightly with a spoonful of chestnut flour, tapping out the excess, the same way you would flour a pan for any cake that likes to stick. This cake has no gluten structure to help it release cleanly, so do not skip this step or rush it, especially around the base where the batter tends to cling stubbornly once baked. If you prefer extra insurance, line the bottom with a small round of parchment paper cut to fit. A well-prepared pan is the difference between a cake that turns out proudly and one that stays behind in pieces.

Give the rested batter a final whisk to loosen it, then fold in most of the drained raisins, pine nuts, and chopped walnuts, saving a small handful of each for scattering on top. Pour the batter into your prepared pan and use a spatula to smooth the surface evenly, since chestnut batter is thick and will not level itself the way a lighter cake batter does. Scatter the reserved raisins, pine nuts, and walnuts over the top, pressing them in very gently so they take root rather than roll off during baking. If you have rosemary, tuck a few needles here and there, a savory whisper that mountain bakers have always loved against the sweetness of the chestnut.

Drizzle a final thread of olive oil over the surface, which helps the top nuts toast rather than burn, then slide the pan into the middle of your preheated oven. Bake for 40 to 45 minutes, resisting the urge to open the door in the first half hour, as chestnut cakes can be sensitive to sudden temperature swings while they set. You will know it is ready when the top has cracked into that classic craggy, sunbaked pattern and a skewer inserted into the center comes out with a few moist crumbs but no wet batter. Those cracks are not a flaw, they are the cake's signature, so do not fuss if it looks a little wild and rustic on top.

Let the cake cool in its pan on a wire rack for at least thirty minutes before attempting to unmold it, because this cake is fragile and quite dense while still warm, and it needs time to firm up as it cools. Run a thin knife around the edge before releasing the springform ring, or gently invert if using a plain cake pan. For the best texture, let it cool completely, even a couple of hours, before slicing, since chestnut cakes only grow more tender and flavorful as they sit. Serve at room temperature in thin wedges, with a spoonful of softly whipped cream or a glass of sweet wine alongside, the way it always appeared at the end of a long mountain Sunday.