Preheat oven to 400 degrees Fahrenheit.
Grease a baking sheet with butter and dust with flour, shaking off excess.
In a large bowl, whisk together 2 cups flour, granulated sugar, baking powder, baking soda and salt.
Add butter; rub in with fingertips until mixture resembles coarse meal.
Mix in chocolate chips and cinnamon-sugar roasted pumpkin seeds.
In a medium bowl, stir together 3/4 cup buttermilk, egg yolk and vanilla; whisk to combine.
Add buttermilk mixture to dry ingredients; stir until combined — the dough will be sticky.
Using floured hands, turn out dough onto a floured work surface, form into a 7- to 8-inch round, and cut into eight wedges.
Use a small spatula or the side of your knife to transfer wedges to prepared baking sheet, spacing 1 inch apart.
It's OK if wedges aren't perfectly shaped.
Brush scones lightly with buttermilk and sprinkle with Demerara sugar.
Bake until scones are golden and a tester inserted into the center comes out clean, which takes about 20 minutes.
Serve warm or at room temperature.