Preheat the oven to 180C/350F/Gas 4. Line an 8x8-inch square baking pan with parchment paper, and set aside.
Place the butter, sugar, cocoa powder, and salt into a large microwave-safe bowl, and heat for 30 seconds. Stir well, then continue heating in 30 second intervals (stirring after each one) until combined and very warm/hot to the touch.
Add the eggs and vanilla, and mix well until combined.
Fold in the flour until fully combined, then gently fold in the chocolate chips and half of the crushed Mini Eggs.
Pour the batter into the prepared pan and spread out evenly. Top with the rest of the crushed Mini Eggs.
Bake for 35 - 40 minutes, or until the centre is no longer jiggly and a toothpick inserted comes out almost clean with a few moist crumbs.
Allow to cool completely in the pan on a wire rack before cutting into bars. For clean, neat brownie slices, I recommend putting the pan in the freezer for an hour before slicing.
Video
Notes
Brownies stay fresh, stored in an airtight container, at room temperature or in the fridge for up to 1 week. They also freeze well for up to 3 months. Thaw overnight in the fridge before serving.