Whisk flour and raisins together in a bowl, then using your fingers, separate any clumps of raisins.
Beat butter and sugars together with an electric mixer until light and fluffy. Add marmalade; beat until blended. Add egg yolk; beat until blended. Add half the flour mixture; mix well. Add sour cream and vanilla; mix well. Add remaining flour mixture; mix well. Add nuts; stir until distributed evenly. Place bowl in freezer 15 minutes to chill.
Preheat oven to 375F. Line 2 large baking sheets with parchment paper.
After chilling, shape dough into 1-inch balls and place on pans 2-inches apart. Flatten balls to 1/4-inch thickness using the palm of your hand or the tines of a fork. Bake 12 to 14 minutes or until cookies are golden. Remove from oven and let cool 2 minutes on baking pans, then transfer cookies to wire racks to cool completely.
To prepare icing, melt butter and cook over medium heat until browned. Pour butter into a small bowl and stir in marmalade. Add powdered sugar and 3 teaspoons water; beat with a spoon until smooth. Add remaining water if necessary in tiny amounts until you reach spreading consistency. Swirl about 1-teaspoonful icing over tops of cooled cookies.