Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
In a large mixing bowl, combine the flour, baking powder, and salt. Mix well.
Add the cold, cubed butter to the flour mixture. Use a pastry cutter or your fingers to blend until the mixture resembles coarse crumbs.
Pour in the milk and stir until just combined. Do not overmix.
Turn the dough out onto a lightly floured surface and knead gently for about 1 minute until it comes together.
Roll the dough into a rectangle about 1/2 inch thick.
Spread the Vegemite evenly over the dough, leaving a small border around the edges.
Sprinkle the shredded cheddar cheese evenly over the Vegemite.
Starting from one long side, carefully roll the dough into a tight log.
Slice the log into 1-inch thick pieces and place them cut-side up on the prepared baking sheet.
Brush the tops of the scrolls with the beaten egg.
Bake for 15-20 minutes or until golden brown and cooked through.
Allow to cool slightly before serving.