Preheat the oven to 180°C/356°F (no fan setting).
Line an 18x24cm (7x10 in) baking pan with parchment paper.
Melt the butter and chocolate together over a double boiler (or microwave in 20-second intervals, stirring in between). Stir in the vanilla extract and let cool slightly.
Whisk the eggs and sugar together in a mixing bowl until slightly pale and frothy. Then, slowly mix in the melted chocolate-butter mixture.
Sift together the flour, cocoa powder, baking powder, and salt. Gently fold the dry ingredients into the wet mixture, avoiding overmixing.
Pour the batter into the prepared pan, smoothing the surface with a spatula. Scatter the chocolate eggs on top, some whole and some halved.
Bake for 25-30 minutes, checking at 25 minutes. A toothpick inserted in the center should come out with a few moist crumbs for a fudgy texture or clean for a cakier texture.
Cool completely before slicing and serving. Enjoy your rich, chocolatey brownies!