Grease several baking sheets or spray with nonstick spray.
In a medium bowl, with electric mixer on medium speed, beat together the flour, baking soda and salt, set aside.
In a large bowl with eletric mixer on medium speed, beat together the butter and brown sugar until well blended and fluffy. Add the eggs, vanilla and beat until evenly incorporated.
Lightly beat in half of the flour mixture.
Add the sour cream and beat until well blended.
Stir in the remaining flour mixture and a generous 3/4 of the pecans.if using.until evenly distributed.
Using a heaping 1/8 measure or coffee scoop, drop the dough onto the baking sheets into evenly shaped mounds.
Space them about 2 1/2" apart. Using a greased hand, pat down the cookies until flattened on top.
Bake cookies, one sheet at a time, in the upper third of the oven for 9-12 minutes, or lightly tinged with brown at the edges and barely firm when pressed in the center. reverse the sheets from front to back halfway through baking to ensure even browning.
Transfer the sheet to a wire rack and let stand until the cookies firm up slightly -- 1-2 minutes.
Using a spatula, carefully transfer the cookies to a wire rack. Let stand until completely cooled.
FROSTING" In a medium saucepan,melt the butter over medium high heat. Bring to a boil and gently simmer, stirring occasionally until it smells very fragrant and turns slightly golden.about 3 minutes. watch carefully,.Stir in brown sugar and cook, stirring for 1 minute more. Stir in 2 1/2 tbls of hot water and the corn syrup until the mixture is well blended and the sugar dissolves. Vigorously stir in the powdered sugar and vanilla until well blended and completely smooth.
Set the frosting aside, stirring occasionally until it cools and stiffens, just enough to spread.2-4 minutes.
Set the wire racks with cookies over wax paper to catch drips. Using a small wide bladed spatula, generously top the cookie tops with frosting.
If pecans were added to the dough, sprinkle a few of the remaining scant 1/4 cup of the pecans over the top of each cookies before frosting sets.
If at any point the frosting stiffens too much to spread, stir in just enough hot water to make it spreadable.Let the cookies stand until the frosting sets, about 45 minutes.
Store in a single layer with wax paper in an airtight container for up to 1 week or freeze for up to 1 month.