01 - Preheat oven to 375°F. Line a 12-cup muffin tin with paper liners or grease lightly.
02 - In a large bowl, whisk together flour, baking powder, baking soda, and salt. Set aside.
03 - In another bowl, mix oil and sugar until combined. Beat in eggs one at a time, then add milk and vanilla extract.
04 - Add wet ingredients to dry ingredients and stir gently until just combined. Do not overmix.
05 - Fold in chopped strawberries until evenly distributed.
06 - In a separate bowl, blend cream cheese, sugar, egg yolk, and vanilla until smooth and creamy.
07 - Spoon about 2 tablespoons of muffin batter into each muffin cup. Add 1 tablespoon of cream cheese filling on top, then cover with another tablespoon of batter.
08 - Swirl gently with a toothpick for a marbled effect if desired.
09 - Bake for 20-22 minutes until muffins are lightly golden and a tester comes out clean, avoiding the cream cheese center.
10 - Cool in tin for 5 minutes, then transfer to a wire rack to cool completely.