Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
In a large mixing bowl, whisk together the flour, baking powder, salt, and sugar until well combined.
Add the cold, cubed butter to the flour mixture. Using a pastry cutter or your fingers, work the butter into the flour until the mixture resembles coarse crumbs.
Pour in the milk and stir until just combined. Do not overmix; the dough should be slightly sticky.
Turn the dough out onto a floured surface and gently knead it a few times until it comes together. Roll the dough into a rectangle about 1/2 inch thick.
Spread the strawberry rhubarb basil jam evenly over the dough, leaving a small border around the edges.
Starting from one long side, carefully roll the dough into a tight log. Pinch the seams to seal.
Slice the log into 1-inch thick rolls and place them cut-side up on the prepared baking sheet.
Brush the tops of the rolls with the beaten egg for a golden finish.
Bake for 20-25 minutes, or until the rolls are golden brown and cooked through.
Allow to cool slightly before serving. Garnish with fresh basil leaves if desired.