1. preheat oven to 350°F and line a 10×15-inch baking tray with parchment paper

2. melt butter and chocolate together until smooth, then whisk in both sugars

3. add eggs one at a time and stir in vanilla

4. sift in flour, cocoa powder, and salt, folding gently until just combined

5. spread batter evenly in the pan and bake for 12–15 minutes until set but still soft

6. while warm, invert brownie onto a towel dusted with powdered sugar and pre-roll to set shape

7. let cool completely rolled, then unroll and spread filling evenly, leaving a small border

8. re-roll the brownie without the towel and place seam-side down on a board

9. frost with buttercream or glaze, using a fork to create bark effect

10. dust with powdered sugar and decorate with holly, cranberries, or edible glitter