Preheat the oven to 340°F (170°C). Generously grease a 10-cup Bundt pan and dust with flour, tapping out the excess.
Make lemon sugar: In a large mixing bowl, combine the granulated sugar and lemon zest. Use your fingertips to rub the zest into the sugar until the mixture is fragrant and slightly damp, 30–60 seconds.
Whisk the dry ingredients in a separate bowl: flour, baking powder, baking soda, and salt.
Build the wet base: To the lemon sugar, whisk in the eggs one at a time until the mixture is pale and thickened. Slowly stream in the oil while whisking to emulsify. Whisk in the sour cream, lemon juice, vanilla, and lemon extract until smooth.
Combine: Add half of the dry ingredients to the wet and stir gently just to combine. Stir in all the buttermilk, then fold in the remaining dry ingredients until no dry streaks remain; avoid overmixing.
Rest the batter for 10 minutes to hydrate the flour and reduce bubbles. Scrape into the prepared pan and tap the pan firmly on the counter 2–3 times to release air pockets.
Bake on the center rack for 42–48 minutes, or until the top springs back lightly and a skewer inserted near the center comes out with a few moist crumbs attached.
Cool the cake in the pan for 12–15 minutes, then turn out onto a wire rack set over a sheet of parchment to catch drips.
While the cake cools slightly, make the warm lemon drizzle: In a small saucepan, combine sugar and lemon juice. Bring just to a simmer over medium heat, stirring until the sugar fully dissolves, 1–2 minutes. Keep warm.
Finish: Poke the warm cake all over with a skewer or toothpick. Brush or spoon the hot lemon syrup over the top and sides in several passes, letting it soak in before adding more. Cool completely before slicing.