Preheat your oven to 375°F (190°C). Line a 12-cup muffin tin with paper liners or grease the cups lightly.
In a large mixing bowl, combine 2 cups of Martha White muffin mix and 1/4 cup granulated sugar.
In a separate bowl, whisk together 1 cup plain Greek yogurt, 1/2 cup milk, 1 large egg, 1/4 cup vegetable oil, and 1 teaspoon vanilla extract until smooth.
Pour the wet ingredients into the dry ingredients. Stir gently with a spatula just until combined. Do not overmix; the batter should be slightly lumpy.
Divide the batter evenly among the 12 muffin cups, filling each about 2/3 full.
Bake in the preheated oven for 16 to 18 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Remove the muffins from the oven and allow them to cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.