Preheat oven to 350°F and line baking sheets with parchment paper.
Melt butter in microwave-safe bowl or on stovetop; let cool slightly.
In a large bowl, combine melted butter and sugar; mix well.
Add eggs one at a time, mixing thoroughly after each addition.
Stir in vanilla extract.
Sift in flour, cocoa powder, baking powder, and salt; fold gently until just combined.
Scoop 1.5–2 tablespoons dough, flatten slightly, place chocolate chunk or ganache in center.
Wrap dough around chocolate and roll into a ball.
Place cookies 2 inches apart on prepared sheets.
Bake 9–12 minutes until edges set but centers remain soft.
Allow cookies to cool on the baking sheet briefly before transferring to wire rack.
Serve warm to enjoy molten chocolate centers.