Preheat the oven to 375°F (190°C) and spray two mini muffin pans with nonstick spray.
Combine 1/2 cup granulated sugar and the orange juice in a small microwave-safe bowl; heat for about 25 seconds, then stir until the sugar dissolves to make the orange syrup. Set the syrup aside and reserve the orange zest.
Sift the 2 cups all-purpose flour, 1 teaspoon baking soda, and 1 teaspoon salt into a medium bowl and set aside.
In a large bowl, beat 1 cup granulated sugar with 1/2 cup (1 stick) room-temperature salted butter and 1 teaspoon orange zest until creamy using an electric mixer.
Add the 3/4 cup sour cream and the flour mixture alternately to the butter mixture, beginning and ending with the flour mixture; beat just until combined after each addition. The batter will be stiff.
Fold in 1/2 cup raisins and 1/2 cup chopped walnuts if using.
Spoon or scoop the batter into the prepared mini muffin pans, filling each cup nearly full.
Bake for 12 to 15 minutes, or until a toothpick inserted in a muffin comes out clean.
Let the muffins sit in the pans for about 10 minutes, then gently remove them and quickly dip the tops in the reserved orange syrup. Transfer to a wire rack and let cool completely.