Preheat over to 375°F and line a muffin pan with liners and set aside.
Cream together the butter and sugar in a large mixing bowl.
¼ cup unsalted butter, ¾ cup granulated sugar
Beat in egg and vanilla. The mixture will be a bit lumpy, that's okay.
1 large egg, 1 teaspoon vanilla extract
In a separate, large bowl, whisk together the flour, baking powder, and salt.
1½ cups all-purpose flour, 2 teaspoon baking powder, ½ teaspoon salt
Slowly add the flour mix, alternating with the buttermilk, until incorporated into the butter mix. Beating until completely combined.
½ cup buttermilk
Gently fold in most OR all of the strawberries. See notes.
1½ cup diced fresh strawberries
Add about ¼ cup of batter to each muffin liner then load up the tops of the muffins with the remaining strawberries.
In a mixing bowl, beat the crumble ingredients until pea-sized crumbs form then sprinkle crumble on the tops of the muffins.
½ cup cold butter, diced small, ½ cup all-purpose flour, ¼ cup light brown sugar, ¼ cup granulated sugar
Reduce oven heat to 350°F and bake muffins for 18 to 20 minutes. Allow muffins to cool in the pan for 5 to 10 minutes before transferring to a wire rack to cool completely.