Preheat oven to 375°F (190°C). Spray an 8½ x 4½-inch loaf pan with nonstick cooking spray.
To the bowl of a stand mixer with a paddle attachment, add the sugar, butter, sour cream, and egg. Beat until creamy. (You could also use a handheld mixer.)
In a separate bowl, whisk together the flour, baking powder, and salt.
With the mixer on low, alternate between adding the flour mixture and the milk, beginning and ending with the flour mixture.
Gently fold in about 1 ¾ cups of raspberries, reserving ¼ cup for the topping.
Pour the batter into the prepared loaf pan. Top with the reserved raspberries.
Bake for 65-70 minutes. The bread is done when an inserted toothpick comes out with a few crumbs, but no wet batter.
Let the loaf cool completely.