To make the brownies: Preheat the oven to 350°F. Lightly coat thirty-four cups of two mini muffin pans with cooking spray.
Place the chocolate and oil in a microwave-safe bowl, and heat in 1-minute increments, until the chocolate is melted and can be easily stirred. (Alternatively, place the chocolate and oil in a small saucepan and slowly warm over low heat until melted.)
In a medium-size bowl, combine the melted chocolate with the tofu, brown sugar, salt, and vanilla. Sift the flour on top, and stir until well combined.
Place about 21⁄2 teaspoons brownie batter per cup, filling each cup two-thirds full.
Bake for 12 minutes. The brownies will look a little wet, and will slightly collapse while cooling; this will create the indentation for the filling. If your brownies don’t collapse within a few minutes, use the curved back of a 1⁄2 teaspoon to indent.
Let cool in the pans on a wire rack, then refrigerate for 45 minutes, to easily remove from the pans. In the meantime, prepare the filling.
To make the filling: Combine the nut butter with the powdered sugar and salt in a small bowl. If your nut butter is on the thin side, add a little extra powdered sugar to thicken. Set aside.
Remove the chilled cups from the pans, and place 1 teaspoon filling per indentation. Sprinkle a tiny handful of chocolate on top, pressing down slightly. Serve chilled. Leftovers may be stored in an airtight container in the refrigerator for up to 1 week.