Preheat oven to 400 degrees F. Spray muffin pan with cooking spray.
Melt butter or coconut oil in microwave on half power. Watch during heating, and stop before completely melted. (Butter will take 30-60 seconds, and coconut oil will take about 15 seconds.) Swirl to melt remaining butter or oil. Set aside.
In a large mixing bowl, stir together flours, salt, baking powder, and baking soda. Gently stir in diced strawberries.
In a medium bowl, whisk together eggs and vanilla. Drizzle in melted butter (or oil) very slowly, whisking the entire time, to prevent hot butter from cooking the eggs. Stir in sour cream, milk, and sugar.
Pour wet ingredients into dry, and stir until just combined. Batter will be very thick.
Scoop batter evenly into muffin tin using a large disher or ice cream scoop if you have one. Bake in preheated oven for 16-18 minutes. Remove from pan and cool on wire rack.
You can also use plain yogurt instead of sour cream.