Preheat the oven to 350 F. In a medium bowl, whisk together flour, salt, and baking soda. In a large bowl, mix together butter, peanut butter and sugar until fluffy. Add in egg and vanilla extract and mix until smooth.
Add in the flour mixture, and mix until it is fully combined. Press the cookie dough evenly into a greased 8-inch square baking dish. Bake for 20-25 minutes.
Remove from the oven and top with chocolate kisses. Cut into bars and serve.