Preheat oven at 325 degrees. Grease an 8 ½ by 4 ½ inch metal loaf pan and line with a strip of parchment paper (see note).
With an electric mixer, beat the butter and sugar until light and fluffy.
Add the eggs one by one, beating for 30 seconds after each egg.
Scrape sides of bowl and beat in vanilla, then beat in the baking powder and salt. Scrape sides of bowl again. Add half of the flour and stir with a heavy duty scraper (or large mixing spoon) until blended, then stir in the sour cream. Add remaining flour and stir until blended, then carefully fold in the blueberries.
Spread the batter in the loaf pan and bake on center rack for about 75 minutes (check at 60). If you are using a smaller loaf pan, put a cookie sheet on the lower rack in case any batter bakes and falls off the side.
My bread took almost 90 minutes in the smaller, more compact pan and 75 minutes in the wider 9x5 inch pan.
Bake until a toothpick or skewer inserted into the center of the loaf is clean. The top should be crusty and golden.
Set the pan on a wire rack and let cool for at least an hour. Carefully remove from pan. Let the bread cool for several hours so it will be easier to slice. It also freezes well. In fact, I thought the structure was better after the loaf had been cooled, frozen and thawed.
Notes
You can use any size loaf pan, but you'll need to keep an eye on the bake time. An 8x4 inch (1 pound capacity) loaf pan was too small and the bread rose up and out to the sides. When baked in a 9x5 inch loaf pan, the loaf had a nice structure and stable shape, but was stubbier. The 8 ½ by 4 ½ was the perfect size. Whatever size you use, check your bread at 60 minutes using a skewer or toothpick, then check every 15 minutes. My 9x5 loaf took 75 minutes and my 8x4 inch loaf took a little longer.