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. Set aside.
03 - Mix oil and sugar in a separate bowl until well combined. Beat in eggs one at a time, then add milk and vanilla extract.
04 - Pour wet ingredients into dry ingredients and stir gently until just combined. Do not overmix to ensure tender muffins.
05 - Fold chopped strawberries into the batter gently until evenly distributed.
06 - Blend softened cream cheese, sugar, egg yolk, and vanilla extract in a separate bowl until smooth and creamy.
07 - Spoon approximately 2 tablespoons of muffin batter into each prepared muffin cup.
08 - Place 1 tablespoon of cream cheese filling on top of the batter in each cup.
09 - Top each cup with another tablespoon of batter to completely cover the cream cheese filling.
10 - Gently swirl with a toothpick to create a marbled effect, if desired.
11 - Bake for 20 to 22 minutes until lightly golden and a toothpick inserted into the batter portion comes out clean.
12 - Let muffins cool in the tin for 5 minutes, then transfer to a wire rack to cool completely before serving.