Prepare a 9" square cake pan by using vegan butter or coconut oil to grease the bottom and sides. Alternatively, line pan with parchment paper. Set aside.
Combine peanut butter and syrup in a microwave-safe bowl. Heat in 10-second increments until the peanut butter softens/melts. Add vanilla and stir until combined.
Pour the rice crispy cereal into a large bowl and then pour peanut butter sauce over the top. Stir until the rice crispies are evenly coated.
Pour the coated rice crispy mixture into the prepared pan and spread it around. You can use your fingers or the greased back of a spoon to press this into the bottom of the pan.
Chocolate Fudge Topping
Next, combine the chocolate chips and vegan butter (or coconut oil) in a microwave-safe bowl. Stir to ensure the chocolate chips are coated and then heat for about a minute. Stir and heat for another 30 seconds until the chocolate chips are melted. Add the milk, one tablespoon at a time, stirring in between until you get the desired spreadable consistency. Spread the chocolate fudge topping over the peanut butter layer.
Cover and place the pan in the fridge to allow it to set for at least 30 minutes (but an hour is more optimal).
A note on salt. You can add up to 1/2 teaspoon of salt to the peanut butter sauce, however, I find most peanut butter has salt added to it, so I don't find it necessary.