Preheat the oven to 350 F. Line a 12 cup muffin pan with paper liners. In a large bowl, whisk flour, sugar, cocoa powder, salt, and baking soda. Add in the peanut butter, eggs, melted butter, and vanilla extract until smooth.
Divide half of the batter between the paper liners. Place one snickers candy bar in each cup and cover with more brownie batter. Bake for 15-20 minutes.