Preheat oven to 350°F. Grease and line a 9x5-inch loaf pan.
Zest and juice the oranges. Set aside measured zest and juice separately.
Beat butter and sugar until pale and fluffy, about 3–4 minutes.
Mix in orange zest and vanilla until fragrant.
Beat in eggs one at a time, scraping the bowl as needed.
Whisk flour, baking powder, and salt in a separate bowl.
Add dry ingredients in two additions, alternating with sour cream and orange juice.
Stir just until combined. Do not overmix.
Spread batter in pan. Smooth top and tap to release air.
Bake 50–60 minutes, until a toothpick comes out clean.
Cool 10 minutes in pan. Turn out and cool completely on a rack.
Whisk powdered sugar with orange juice and zest until pourable.
Drizzle glaze over cooled cake. Let set 15 minutes before slicing.