Use fresh or frozen (don’t thaw before using); whichever you have on hand. Some call this coffee cake because it’s great with coffee. I like it for breakfast. It’s a thick, heavy buttery cake that’s perfect summer, winter, fall…well, you get it. It’d be perfect for a weekend or holiday.
This cake freezes really well when wrapped in airtight wrap. Use within 2 months.
Preheat oven to 350° F.
Spray a 9 x 9-inch baking pan with nonstick spray; set aside.
Make the topping: In a small bowl, stir oats, flour, sugar, cinnamon and salt. Add butter and blend until crumbly; set aside.
Make the cake batter: In a medium bowl, stir together flour, baking powder, and salt; set aside.
In a large mixing bowl, add butter and sugar; beat until fluffy (about 1 minute).
Add eggs, sour cream, half-and-half and vanilla; beat until well blended, about 1 minute.
Add the flour mixture; beat on low speed just until combined, scraping down the sides with a rubber spatula, about 30 seconds. Increase speed to medium and mix just until well blended, about 30 seconds.
With a rubber spatula, gently fold in the blueberries.
Turn batter into prepared pan.
Sprinkle the topping mixture evenly on top; press lightly.
Bake until a wooden pick inserted in the center comes out clean, 40 to 45 minutes.
Let cool in pan 30 minutes before serving.