Preheat the oven to 350 F. In a medium bowl, whisk together flour, cocoa powder, salt, and baking soda. In a large bowl, combine butter with sugar until fluffy. Add in egg and vanilla extract and mix until it is smooth.
Add in the flour mixture, mix until it is fully combined. Fold in the chocolate chips. Roll the cookie dough into balls, and place them onto a large ungreased baking sheet. Bake for 10-12 minutes.
Remove from the oven, and place one heart chocolate on each cookie.