Step 1

Pulse flour, sugar, and salt in a food processor to combine. Add butter and pulse until mixture resembles coarse meal with a few pea-size pieces of butter remaining.

Step 2

Transfer to a large bowl and add buttermilk. Mix with a fork, adding more buttermilk by the tablespoon if needed, just until a shaggy dough comes together; knead very lightly until no dry spots remain. Pat into a disk and wrap in plastic. Chill at least 4 hours.

Step 3

DO AHEAD: Dough can be made 2 days ahead. Keep chilled.

Step 4

Preheat oven to 325°F. Roll out pie dough on a lightly floured surface to a 14″ round. Transfer to a 9″ pie dish, allowing dough to slump down into dish. Trim dough, leaving about 1″ overhang. Fold overhang under and crimp edge. Prick bottom all over with a fork. Freeze 15 minutes.

Step 5

Line crust with parchment paper or foil, leaving an overhang, and fill with pie weights or dried beans. Place pie dish on a rimmed baking sheet and bake until crust is dry around the edge, 20–25 minutes. Remove parchment and weights; bake until surface looks dry, 10–12 minutes longer.

Step 6

Meanwhile, blend egg yolks, eggs, buttermilk, sugar, lemon zest, lemon juice, salt, and saffron in a blender until smooth. With motor running, add 2 tablespoons flour, then butter. Tap blender jar against countertop to burst any air bubbles in filling and pour into warm crust.

Step 7

Bake pie, rotating halfway through and covering edges with foil if they brown too much before filling is done, until filling is set around edge but center jiggles slightly, 55–65 minutes. Transfer pie dish to a wire rack and let pie cool. Serve pie with whipped cream.

Step 8

DO AHEAD: Pie can be baked 2 days ahead. Keep at room temperature up to 6 hours; cover and chill to hold longer.