Preheat your waffle iron according to manufacturer's instructions until fully heated.
In a large bowl, whisk together the flour, sugar, baking powder, and salt until evenly combined.
In a separate medium bowl, whisk the eggs until lightly beaten. Add the milk, peanut butter, oil, and vanilla extract, whisking vigorously until the peanut butter is fully incorporated and the mixture is smooth.
Pour the wet ingredients into the dry ingredients and stir gently with a spatula until just combined. Small lumps are fine — overmixing will create tough waffles. Let the batter rest for 3-5 minutes.
Lightly spray the waffle iron with non-stick cooking spray. Pour the recommended amount of batter onto the center of the iron (usually 1/2 to 3/4 cup, depending on your iron size).
Close the lid and cook for 4-5 minutes without opening, until the steam stops escaping and the waffle is golden brown. Use a fork to gently lift the waffle out.
Repeat with remaining batter, keeping finished waffles warm in a 200°F oven on a wire rack if serving all at once.
Serve immediately with your favorite toppings, or cool completely on a wire rack before storing.