Step 1: Preheat your oven to 350°F (175°C). Grease a 12-inch pizza pan or a round baking sheet.
Step 2: In a mixing bowl, whisk together the melted unsweetened chocolate, vegetable oil, and granulated sugar until smooth.
Step 3: Beat in the eggs one at a time, mixing well after each addition.
Step 4: Gently fold in the all-purpose flour and salt until just combined. Do not overmix.
Step 5: Spread the brownie batter evenly in your prepared pan, reaching the edges.
Step 6: Bake for about 18-22 minutes, or until the edges are set but the center still looks a little soft and slightly underbaked.
Step 7: As soon as it comes out of the oven, sprinkle the semi-sweet chocolate chips evenly over the top. Let them sit for about 2 minutes to soften from the heat.
Step 8: Use a spatula or knife to gently spread the melted chocolate smoothly over the entire surface of the brownie base.
Step 9: Generously press the chopped candy bars and Reese's Pieces (or M&M's) firmly into the warm melted chocolate layer.
Step 10: Warm the peanut butter slightly (microwave for 15-30 seconds) and drizzle it all over the top of your candy-covered pizza.
Step 11: Allow the pizza to cool completely (1-2 hours) before slicing it into wedges. This allows the brownie and toppings to set for cleaner slices.