5 tablespoons unsalted butter, use divided
2 cups light brown sugar
1 tablespoon pure vanilla extract
1/2 cup plus 3 tablespoons heavy cream, use divided
1 cup SunButter, any smooth variety
1-3/4 cups powdered sugar
3 tablespoons corn syrup or agave
1 cup semisweet chocolate chips
Line an 8-inch square cake pan with parchment paper with a 2 inch overhang of paper on all sides.
Melt 4 tablespoons butter in a medium saucepan over medium-high heat. Add the brown sugar, vanilla, and the 1/2 cup cream. Bring to a boil. Let boil for 2 minutes, stirring constantly. Add the SunButter and stir until smooth. Take off the heat and let cool for 5 minutes.
Put the SunButter mixture in a mixer preferably fitted with a paddle attachment. Mix on medium-low speed and gradually add the powdered sugar. Mix until everything is incorporated and smooth. Put the mixture in the prepared pan and smooth the top with a spatula.
In a small saucepan, melt the remaining 1 tablespoon butter with the corn syrup and chocolate chips. Add the remaining 3 tablespoons of cream and mix until smooth. Pour over the top of the SunButter fudge and refrigerate until firm, at least 2 hours.
Cut into small squares and serve.