1. Spray the inside of a slow cooker with baking spray and lay a large piece of parchment paper in the bottom, leaving overhang on each side.
  2. Grease the parchment paper with baking spray as well. Combine flour, cocoa powder, baking powder, and salt in a medium bowl and whisk.
  3. Melt together butter and dark chocolate. Combine chocolate mixture, granulated sugar, eggs, and vanilla extract in a large bowl and whisk until smooth.
  4. Add in the dry ingredients and stir just until combined. Add in half of the chocolate morsels and fold to incorporate into the batter.
  5. Pour brownie batter into the slow cooker, sprinkle on remaining chocolate morsels, cover, and cook on LOW for 3-4 hours, until center is set but still moist.

  6. Uncover the slow cooker in the last 30 minutes or so of cooking.