Preheat oven to 375°F (190°C) and line a 12-cup muffin tin with paper liners.
In a medium bowl, beat the softened cream cheese, 1/4 cup sugar, egg yolk, and 1/2 teaspoon vanilla until smooth; set aside for the filling.
In a large bowl, whisk together the flour, 1/2 cup sugar, baking powder, and salt.
In a separate container, whisk the milk, egg, melted butter, and 1 teaspoon vanilla extract until emulsified.
Fold the wet ingredients into the dry ingredients until just combined; do not overmix.
Gently fold the diced strawberries into the batter.
Spoon approximately 2 tablespoons of batter into each prepared muffin cup.
Add 1 tablespoon of the cream cheese filling to the center of each cup.
Distribute the remaining batter over the cream cheese filling to seal the centers.
Bake for 22 to 25 minutes or until the muffin tops are golden and spring back when touched.
Cool in the tin for 5 minutes before transferring to a wire rack for complete cooling.