01 - Preheat oven to 375°F. Line a 12-cup muffin tin with paper liners or grease lightly with cooking spray.
02 - Whisk together flour, baking powder, baking soda, and salt in a large bowl until thoroughly combined.
03 - In a separate bowl, whisk oil and sugar until blended. Beat in eggs one at a time, then incorporate milk and vanilla extract.
04 - Pour wet mixture into dry ingredients and fold gently until just moistened. Avoid overmixing to prevent tough muffins.
05 - Gently fold chopped strawberries into the batter until evenly distributed.
06 - Beat softened cream cheese, sugar, egg yolk, and vanilla in a small bowl until completely smooth and creamy.
07 - Place 2 tablespoons muffin batter into each cup. Add 1 tablespoon cream cheese filling, then cover with another tablespoon of batter.
08 - Swirl gently with a toothpick through the batter to create a marbled pattern, if desired.
09 - Bake for 20 to 22 minutes until tops are lightly golden and a toothpick inserted into the cake portion comes out clean.
10 - Let muffins rest in the tin for 5 minutes, then transfer to a wire rack to cool completely before serving.