Preheat oven to 325°. Spray a 9x5-inch loaf pan with baking spray with flour. Line pan with parchment paper, letting excess extend over sides of pan.
In a large bowl, whisk together sugar and melted butter. Whisk in sour cream, eggs, lemon zest, and vanilla. In a medium bowl, whisk together flour, rosemary, baking powder, baking soda, and salt. Add flour mixture to sugar mixture, whisking just until combined. Spoon batter into prepared pan and spread evenly with an offset spatula. Tap pan firmly on counter a few times to remove any air bubbles.
Bake until top is dry and golden brown, 45 to 50 minutes. Cover with foil and bake until a wooden pick inserted in center comes out clean, 10 to 15 minutes more. Let cool in pan for 10 minutes. Using excess parchment as handles, remove from pan. Let cool completely on a wire rack. Serve at room temperature with sweetened whipped cream.
Recipe by Southern Lady Magazine at https://southernladymagazine.com/lemon-rosemary-loaf-recipe/