Preheat oven to 350°F (175°C). Line baking sheets with parchment paper.
In a large bowl, cream together the softened butter, granulated sugar, and brown sugar until light and fluffy.
Beat in the egg and vanilla extract until well combined.
In a separate bowl, whisk together the flour, baking soda, and salt.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Do not overmix.
Place the chopped pecans in a shallow dish.
Roll the cookie dough into 1-inch balls. Roll each ball in the chopped pecans.
Place the pecan-coated balls on the prepared baking sheets, about 2 inches apart.
Bake for 8-10 minutes, or until the edges are lightly golden.
Remove the baking sheets from the oven. Immediately press one Hershey's Kiss into the center of each warm cookie. The heat will help it melt slightly and adhere.
Let the cookies cool on the baking sheets for a few minutes before transferring them to a wire rack to cool completely.
Notes
Store cooled cookies in an airtight container at room temperature for up to 3 days.