1/2 cup whole milk, brought to room temperature (if you can remember)
2 cups blueberries (or raspberries)
1/2 cup sugar
1/3 cup flour
1 teaspoon cinnamon
1/4 teaspoon kosher salt
4 tablespoons cold butter (1/4 cup)
1. Preheat the oven to 375 degrees. Butter and flour a 9-inch square baking pan.
2. Whisk together the flour, baking powder and salt, and set aside.
3. Cream the sugar and butter until light and fluffy—about 3 to 5 minutes. Add one egg, mix and scrape down the sides of the bowl. Then mix again to thoroughly blend.
4. On the lowest speed, add 1/3 of the flour mixture, then half of the milk (about 1/4 cup), and repeat, ending with the flour. Mix until the ingredients have blended.
5. Scrape the sides of the bowl and fold by hand, then add the blueberries (try not to crush them). The batter will seem very thick and bursting with berries.
6. Spread into prepared pan.
7. Make the topping. Cut the butter into little pieces (pea size).
8. Whisk the sugar, flour, cinnamon and salt. Add the butter and with your hands, mix the crumb to incorporate the butter by picking it up in handfuls and rubbing it together so that the butter (or some of it) becomes incorporated. Do this a few times.
9. Place crumb mixture evenly over batter and bake for about 42 to 46 minutes, checking often. It is perfect warm out of the oven—although it might fall apart. Try to catch the crumbs.