Preheat the oven to 350°F (180°C). Line the pan with foil or parchment paper.
Melt the butter in a small pan and let it cool slightly.½ cup unsalted butter
Chop the mini eggs and walnuts. Keep the pieces chunky. Be careful, the shells are hard and can slip.1½ bags mini eggs + ½ cup walnuts
Mix: In a bowl, mix the melted butter and egg.butter + 1 large egg
Add brown sugar and vanilla and whisk until smooth.¾ cup light brown sugar + 2 teaspoons vanilla extract
Add flour and salt. Stir briefly, just until combined. Don’t overmix.1 cup all-purpose flour + ¼ teaspoon fine sea salt
Fold in the chopped mini eggs, chocolate chips, and walnuts.mini eggs + ½ cup semisweet chocolate chips + walnuts
Bake cookie bars: Transfer the dough to the pan and smooth the top. Press a few extra mini eggs on top. Bake for 25–28 minutes. A toothpick inserted in the center should come out with a few crumbs. Mine took 26 minutes.
Let cool completely in the pan before slicing.
Notes
Measurements: I recommend using a digital kitchen scale in baking; it guarantees the best results.
Mini eggs: One bag of mini eggs is about 90 g (3 oz). Use one bag in the dough and about half a bag on top. If you prefer, you can chop all the eggs and skip adding whole ones on top.