Place the 2 cups sliced strawberries, 2 cups sliced rhubarb, ⅔ cup sugar, and ½ teaspoon cinnamon in a 9x9-inch baking dish. Mix to combine.
Bake for 20 minutes, then remove from the oven. The fruit will seem like it has a lot of liquid but some of that will cook off with the next round in the oven.
While the strawberry rhubarb mixture is baking, whisk together 2 cups flour, 2 tablespoons sugar, 2 teaspoons baking powder, and ½ teaspoon salt. Cut in 4 tablespoons butter with a fork or pastry blender.
Whisk ¼ –⅓ cup milk (start with ¼ cup) and 1 egg together, then add it to the flour mixture. Stir to form a thick dough. You may need a splash or two more milk to get it to hold together. Do not over mix or it'll get tough once baked.
Drop dough by tablespoons onto fruit. Bake for 18–22 minutes, or until the cobbler topping is golden brown.
Serve with whipped cream or ice cream, or just a drizzle of plain heavy cream over the top.
Notes
You can use more or less of each fruit as you like. For example, you can try it with 1 cup of strawberries and 3 cups of rhubarb. If you use more rhubarb, you'll need to add a bit more sugar. If you use less rhubarb, reduce the sugar. You can swap the cinnamon with the zest of one orange or one lemon. Leftovers will keep on the countertop for 2–3 days or for up to one week in the fridge, tightly covered. Reheat the cobbler in the microwave or the oven. Original microwave instructions if you're curious (important note: I did NOT test this): cook for 10 minutes on high for fruit, then 15 minutes on 30% power once the cobbler topping is added.