Prepare the raspberry sauce by cooking the fresh raspberries until softened and thickened. Let cool.
Add the sugar and vegetable oil to a mixing bowl.
Add the egg and whisk until combined.
Add the vanilla extract and mix well.
Add the yogurt and whisk until smooth.
In a separate bowl, whisk together the all-purpose flour, baking powder, and salt.
Gradually add the dry ingredients to the wet mixture.
Mix until a smooth batter forms.
Divide the batter evenly among the lined muffin cups.
Add the raspberry sauce over the batter and gently swirl.
Prepare the streusel by combining the all-purpose flour, granulated sugar, and melted butter until crumbly.
Sprinkle the prepared streusel topping over each muffin.
Bake at 180°C (350°F) for 18–22 minutes, or until a toothpick inserted into the center comes out clean.
Let the muffins cool in the pan for a few minutes, then transfer to a wire rack and let cool completely. Serve and enjoy.
