Preheat your oven to 350°F and grease an 8-inch round cake pan, or line it with parchment for easy removal.
Warm the milk in a small saucepan over low heat until just barely steaming — about 140°F if you have a thermometer, but don't bother if you'd rather not wrestle one out. Pour over the crushed saffron threads and let them steep while you prep everything else. The milk should turn a vivid golden-orange within five minutes.
In a medium bowl, whisk together the flour, baking powder, and salt until evenly combined. Set aside.
Using an electric mixer on medium speed, beat the softened butter and sugar together for about 3 minutes until pale and creamy — this is where you'll get that light crumb structure.
Add the eggs one at a time, mixing well after each addition. Scrape down the sides of your bowl with a spatula to make sure everything's incorporated evenly. Beat in the vanilla extract.
Pour in the saffron-infused milk (straining out the threads if you prefer — I leave mine in for texture). Mix on low until just combined; overmixing at this stage makes the cake dense instead of tender.
Add about a third of your dry ingredients and mix gently, then pour in half the liquid, followed by another third of dry, the rest of the liquid, and finish with whatever dry ingredients are left. Stop mixing as soon as no streaks of flour remain — you want the batter to look slightly lumpy, not silky smooth.
Pour into your prepared pan and sprinkle with turbinado sugar if using. Bake for 30-35 minutes until a toothpick inserted in the center comes out clean or with just a few moist crumbs clinging to it. The cake should pull away slightly from the sides of the pan.
Let cool in the pan for about ten minutes, then turn out onto a wire rack to finish cooling completely before slicing.