Preheat oven to 350 degrees. Line a baking sheet with parchment paper or a silicone baking mat. Set aside.
In a large mixing bowl add the butter, beat until smooth and creamy. Add the light brown sugar and mix until combined and fluffy.
Add the eggs one at a time, mixing in between. Add in the sour cream and maple syrup, mix until completely combined.
In a medium size bowl combine the flour, salt and baking soda. Stir with a fork. Then slowly pour the dry ingredients into the wet ingredients, slowly mixing until just combined.
Using a cookie scoop or spoon, spoon about 2 tablespoons of the cookie dough onto the baking sheet.
Bake for about 12 minutes until the cookies are turning golden on the edges. Remove from the oven and allow to cool on the pan for about 3-4 minutes, then remove to continue cooling on a wire rack. Repeat this process until all the cookie dough has been baked. This will make about 3 dozen cookies.
Once the cookies are cooled prepare the frosting.
Brown Butter Frosting
Add the butter to a small sauce pan. Heat over medium heat, butter will melt. Stir while the butter continues to cook. It will foam and bubble while cooking. Continue to stir cooking over medium heat. Once the butter starts to form brown bits on the bottom of the pan, and the foam starts to go away, you will notice a nutty smell coming from the butter. Remove from heat and pour the butter and all the browned bits into a medium size bowl.
Allow the butter to cool for several minutes before moving onto the next step.
Once the butter is cooled add in the powdered sugar, heavy cream and vanilla extract. Stir until smooth and creamy. If needed add more powdered sugar or heavy cream to reach desired consistency.
Spread the frosting over the top of the cooled cookies.
Store the cookies at room temperature in a sealed container, will keep for 4-5 days.