Preheat oven to 350°F.

Line a 9×13-inch baking pan with parchment paper, leaving overhang on the sides.

Set aside while you mix the batter.

In a heatproof bowl or saucepan over low heat, melt the butter and chopped chocolate together. Stir until smooth and glossy. Let the mixture cool slightly.

Whisk the granulated sugar, brown sugar, eggs, and vanilla into the melted chocolate mixture. Mix until glossy and fully combined.

Sift in the flour, cocoa powder, and salt. Fold gently until no dry streaks remain. Do not overmix.

Spread the batter evenly into the prepared pan.

Bake for 28 to 34 minutes, or until the center is just set. A toothpick should come out with moist crumbs.

Let the brownies cool completely in the pan. Lift them out using the parchment overhang. Transfer to a flat surface for decorating.

Beat the softened butter until creamy.

Gradually mix in the powdered sugar. Add vanilla and enough cream or milk to create a thick, pipeable frosting.

Divide the frosting into 4 bowls. Tint one pink, one blue, one yellow, and one green.

Transfer to piping bags or keep ready for spooning.

Slice the cooled brownie slab into 12 squares. Wipe the knife between cuts for neater edges. Arrange the squares for decorating.

Pipe or spoon a nest-like swirl of frosting on each brownie square. Leave a slight dip in the center. Use mixed pastel colors across the batch.

Melt the white chocolate or candy melts until smooth. Drizzle lightly over the frosted brownies. Let the drizzle settle for a minute.

Add pastel sprinkles over each brownie. Place 2 mini candy eggs in the center of each frosting nest. Add chick candies if using, then let the brownies set for 15 to 20 minutes before serving.