- Preheat the oven to 425℉ or 220℃. Line a muffin tin with muffin cups before setting aside.  
- In a large bowl, mix together the melted butter, strawberry Kefir (or thinned Greek yogurt), sugar, eggs and vanilla extract.  
- Next, fold in 2 cups of the all purpose flour, baking powder and salt until just combined. Be sure not to overmix.  
- Slowly fold in the chopped chocolate (or chocolate chips), chopped strawberries and remaining 1 tablespoon of all purpose flour.  
- Scoop the batter into the prepared muffin cups, filling just shy of the top of each cup.  
- In a small bowl, combine the melted butter, flour and sugar for the streusel topping until it comes together in small clumps. Sprinkle the top of each muffin cup with a bit of this topping.  
- Bake for 5 to 7 minutes at 425℉, then, without opening the oven door, reduce the heat to 350℉ (or 180℃) and bake for another 15 minutes or until a toothpick inserted into the center of the muffin comes out clean or with only a couple of crumbs.  
- Remove from the oven and allow to cool for 10 minutes before transferring to a rack to fully cool or a plate to serve. Muffins can be stored at room temperature for up to 3 days (if they last that long!). Enjoy!