Preheat the oven to 350° and spray a 9 x 13 baking dish with non-stick cooking spray or line with foil and lightly spray, leaving the aluminum foil hanging over the edge a bit.
In a medium bowl, whisk flour, cocoa powder, baking powder and salt together. Set aside.
In a large bowl, whisk eggs, sugar butter, and vanilla until combined.
Add dry ingredients to the wet ingredients and stir just until combined.
Next, fold chocolate chunks and chopped walnuts in the brownie batter.
Pour the batter into the prepared baking dish and spread evenly.
Top with edible heart sprinkles.
Bake for 25-30 minutes or until a toothpick inserted in the center comes out with moist crumbs attached.
Let the brownies cool in the pan. Cut into 12 pieces, or grab both sides of the foil, lift out of the pan, and cut into 12 pieces.
Serve with a scoop of vanilla ice cream.