Preheat your oven to 415°. Grease muffin tins or line them with paper liners. Set aside.
In a mixing bowl, combine eggs and sugar. Mix until the mixture becomes frothy. Then, add melted butter and sour cream to the mixture.
In a separate bowl, sift together baking powder, baking soda, salt, and flour.
Gradually add the dry ingredients into the wet ingredients, along with lemon zest. Folding them together. Pour in the buttermilk and continue folding until well combined.
In another bowl, toss the blueberries and cherries with 2 tablespoons of flour. Gently fold the fruit mixture into the batter.
For the streusel topping, melt butter and mix it with brown sugar, white sugar, flour, cinnamon, and granola. Stir until the mixture becomes clumpy and sand-like.
Spoon about 1/4 cup of batter into each muffin tin, then sprinkle the streusel topping over the batter.
Bake the muffins in the preheated oven for 5 minutes, then rotate the muffin tin and reduce the temperature to 375°F (190°C). Continue baking for an additional 15 minutes or until the muffins are golden brown.
Once baked, allow the muffins to cool in the pan for 5 minutes before serving. Enjoy!