Preheat your oven to 350° F, and grease or line an 8x8 square baking dish with parchment paper.
Chop 4 oz semi-sweet baker's chocolate into small pieces and place them into a microwave-safe bowl. Melt the chocolate in 20-second intervals, stopping to mix with a spoon, until fully melted.
In a large mixing bowl, add 1/2 cup melted, salted butter and 1 cup white sugar and whisk until well combined.
Add in 2 large room temperature eggs and 1 teaspoon vanilla extract and whisk vigorously for about 5 minutes or until light in color and has volume.
Add the melted chocolate to the mixing bowl and stir until well combined.
Using a fine sifter, sift in 3/4 cups all purpose flour (spooned and leveled), 1/4 cup unsweetened cocoa powder, and 1/2 tsp salt.
With a rubber spatula, mix the wet and dry ingredients until just combined. Do not overmix.
Once mixed, gently fold in 1 cup mini eggs.
Pour the batter into your prepared baking dish, and spread it in an even layer. Sprinkle extra eggs over the top and press them slightly into the batter.
Bake for 25-28 minutes, or until a toothpick inserted into the middle comes out clean.
Let the brownies cool completely before removing them from the pan or slicing.