01 - Preheat oven to 375°F. Line a 12-cup muffin tin with paper liners or grease lightly with cooking spray.
02 - In a large mixing bowl, whisk together flour, baking powder, baking soda, and salt until thoroughly blended.
03 - In a separate bowl, whisk oil and sugar until combined. Beat in eggs one at a time, then stir in milk and vanilla extract until smooth.
04 - Pour wet mixture into dry ingredients. Fold gently with a spatula just until combined—do not overmix or muffins will become tough.
05 - Gently fold chopped strawberries into the batter, taking care not to crush the fruit.
06 - In another bowl, beat softened cream cheese, sugar, egg yolk, and vanilla until completely smooth and creamy.
07 - Spoon approximately 2 tablespoons of muffin batter into each prepared cup. Add 1 tablespoon of cream cheese filling center, then top with another tablespoon of batter to cover.
08 - Gently swirl a toothpick through the batter once to create a marbled pattern, if desired.
09 - Bake for 20–22 minutes until tops are lightly golden and a toothpick inserted into the batter (not the cream cheese center) comes out clean.
10 - Let muffins cool in the tin for 5 minutes, then transfer to a wire rack. Cool completely before storing.