Preheat oven to 350°F / 177°C.
Spray a muffin pan with nonstick cooking spray (or use muffin liners).
In a small mixing bowl, combine flour, baking powder, and a pinch of salt. Set aside.
In a medium mixing bowl, whisk together 1/2 cup sugar, milk, yogurt, vegetable oil, 1 teaspoon vanilla, and vinegar until evenly combined.
Gently fold dry ingredients into wet ingredients until no dry spots remain (do not overmix).
Spray a cookie scoop or ¼ cup measuring cup with nonstick cooking spray (this will prevent the batter from sticking). Scoop up batter and divide it between spaces in the prepared muffin tin, filling each space about halfway. Sprinkle each shortcake with Demerara sugar (if using).
Bake until a tester inserted into one of the cakes comes out clean, 14 to 16 minutes.
Allow cakes to cool in the muffin tin. Serve immediately or store at room temperature for up to 3 days.