Preheat the oven to 375 degrees F. Line 2 large baking sheets with parchment paper, or lightly grease with butter.
Mix the dry ingredients. In a medium bowl, stir together the flour, granulated sugar, baking powder, and salt.
Mix the wet ingredients. In another medium bowl, whisk together the 1/3 cup of milk, oil, egg, and egg yolk, and 1 teaspoon vanilla until well combined.
Combine the ingredients. Make a well in the center of the dry ingredients. Add the wet ingredients to the middle of the dry ingredients, and stir until nearly blended. Some lumps are ok. Gently fold in the blueberries until everything is just combined.
Bake the muffins. Using a large ice cream scoop or spoon, spoon about 3 tablespoons of the batter onto the prepared pans for each top, leaving about 2 inches of room between each. Bake for 10 to 14 minutes, or until a toothpick inserted into the middle comes out clean and muffins are slightly browned around edges. Cool slightly, then remove muffins from the pans and cool on a wire rack.
Make the drizzle. Meanwhile, in a small bowl, mix together the cream cheese, powdered sugar, and 1/4 teaspoon vanilla. Slowly stir in the milk, a little at a time, until well blended and a thin consistency. With a fork, drizzle over the cooled muffins.
SNAPPY TIPS: For a crunchier muffin, sprinkle a little crystal or turbinado sugar on top of the muffin tops before baking.SNAPPY SUBSTITUTIONS: Instead of vanilla, you could add a little orange juice and orange zest.