Preheat oven to 350°F (180°C) and line a baking sheet with parchment paper.
Beat softened butter, peanut butter, brown sugar, and granulated sugar until fluffy.
Mix in the egg and vanilla extract until combined.
Whisk flour, baking soda, and salt in a separate bowl, then add to wet ingredients and mix until combined.
Roll dough into balls and gently flatten into rounds or heart shapes.
Bake cookies for 10–12 minutes until edges are set but centers remain soft, then let cool briefly.
Melt chocolate chips with coconut oil until smooth.
Spoon or pipe melted chocolate into heart shapes on each cookie.
Allow chocolate hearts to set at room temperature or chill for 15 minutes until firm.