Prep: Start by preheating the oven to 350 degree F.
Then, line a muffin pan with paper or silicon cups. If you don't have either of these, spray the muffin pan very well with non-stick cooking spray. Set aside.
Clean and prep your fruit, cut up only the strawberries into small chunks.
Muffin batter: In a large mixing bowl, cream together the butter and sugar until nice and fluffy. Next, beat in the egg until fully combined.
In a separate small bowl, sift together the flour, baking powder and salt. If you don't have a sieve, a whisk will work just fine.
After that, add the flour mixture and the milk to the large bowl with the butter mixture. Alternating by adding flour, then milk, start and end with the flour being added.
Lastly, fold in the blueberries, strawberries and white chocolate chips. Proceed to pour the batter into greased or paper-lined muffin cups, filling about 3/4 of the way.
Make streusel: In a medium size bowl, combine all the streusel ingredients until mixed well.
Using a fork, sprinkle the streusel over the top of the unbaked muffin cups. Make sure to spread the mixture out evenly over each muffin, giving them all plenty of streusel love.
Bake: Place muffin pan in the preheated oven and bake for 30 minutes at 350degrees F.
Let the muffins cool for about 10 minutes, if desired, melt the white chocolate chips in the microwave and drizzle over the tops of the muffins. Let them cool for a few more minutes. Serve fresh and warm, enjoy!