Preheat oven to 375° F Prepare a 10 inch cast iron skillet or 9 inch cake pan by either spraying with either nonstick spray or coating lightly with butter.
Place sliced peaches and strawberries in a medium bowl. Sprinkle with sugar. Stir together and set aside.
To make streusel, whisk together flour, sugar, cornmeal, and just a tiny pinch of salt. Toss softened butter in the dry ingredients then, using your fingers or a pastry cutter, combine them together until you have a texture of wet sand. You want some finer parts and some clumps. You’ll know it’s done when you can press down and it all seems to stick together.
In a medium bowl, whisk together flour, cornmeal, sugar, baking powder, baking soda, and salt.
Using a hand mixer, or stand mixer, cream together butter and sugar until light and fluffy, about 3 minutes. Mix in eggs, one at a time, and then the vanilla. You can't over-mix at this point. Add yogurt and milk and mix in.
Add the dry ingredients to the wet ingredients and, using a spatula, mix together just until all the dry ingredients have been incorporated.
Pour half of the batter in your pan. Hand place half of the peaches and strawberries on top. Cover with the remaining batter and arrange the last of the fruit on top. Leave the juice behind. Add it to a glass of iced tea.
Sprinkle the streusel on top of the cornbread and bake at 375°F for 35-40 minutes, or until a skewer poked in the middle comes back clean.
Allow to cool for 10-15 minutes before serving.