In a small bowl, whisk together the egg, sour cream and vanilla until well combined. Set the mixture in the fridge.
In a medium-sized mixing bowl, add the flour, baking powder, salt, and sugar. Cube up the cold butter stick and add it to the dry ingredients.
Using a pastry cutter or your fingers, cut the butter into the flour mixture until the butter pieces are quite small.
Make a well in the center of the dry ingredients, then pour in the wet ingredients mixture. Lightly mix the ingredients together in the bowl until you have a shaggy dough.
Use your hands to lightly knead the scone dough together just until it becomes a cohesive ball.
Turn the dough out on to a lightly floured surface.
Using a rolling pin to roll the dough out to a 10" x 14" (25 x 35 cm) rectangle.
In a small microwave safe bowl, melt the butter. Then, mix in the brown sugar and cinnamon.
Carefully spread the brown sugar cinnamon mixture over the scone dough into an even layer.
From the longer side of the rectangle, carefully roll up the scones into a tight cylinder (the same way you would roll cinnamon rolls.)
Wrap the dough tightly in plastic wrap and let it sit in the freezer for at least 1 hour.
When you're ready to bake the scones. preheat the oven to 425°F / 220°C. Line a cookie sheet with parchment paper or a silicone baking mat.
Slice a small sliver of dough off of both ends of the log to reveal the cinnamon swirl. Slice the log into 4 equally sized pieces, then slice each piece on a diagonal to create a triangle shaped piece.
Evenly space the scones out on the baking sheet, leaving space between each for spreading.
If desired, you can brush a little bit of heavy cream on top of the scones to encourage the tops to brown. Bake for 12-15 minutes, or until the scones start to turn golden brown on top and on the bottoms. Note that some of the scones may flatten and some may bake up straight - this is normal and both ways are delicious!