Preheat oven to 350 degrees and grease 2 baking sheets or line them with parchment paper.
Sift flour and baking soda together into a bowl. Add salt. Set aside.
Using an electric mixer, beat together the brown sugar and butter until fluffy.
Add eggs one at a time and vanilla extract. Beat until evenly mixed, scraping down the sides of the bowl.
Lightly beat in half of flour mixture.
Beat in sour cream until blended well.
Add remaining flour mixture and pecans and beat until mixed.
Using a 1/8-cup measure cup or ice cream scoop, drop dough in even mounds on prepared sheets, leaving 2 1/2 inches between cookies. Lightly flatten the tops of cookies using your hand or the back of a spoon.
Bake 1 sheet at a time placing in the upper third of the oven for 9 to 12 minutes. Edges should be turning light gold and center should be just barely firm. Let cool on pans for 2 minutes before removing to wire racks to cool completely.
For frosting, melt butter in a medium saucepan over medium-high heat. Simmer butter, stirring occasionally until it turns slightly golden and smells very fragrant, about 3 minutes.
Add brown sugar and cook 1 minute while stirring.
Stir in hot water and corn syrup until well mixed and sugar dissolves.
Vigorously stir in powdered sugar and vanilla extract until completely smooth. Add sea salt.
Frost cookies before frosting sets and sprinkle with pecans.