This is a Barefoot Contessa Recipe, but Pioneer Woman did a step by step a while back. If you need more direction, go there.
2 1/4 sticks butter
3 cups sugar
6 eggs
1 cup sour cream (not low fat, Jeffrey wouldn't like that, now would he?)
1 1/2 teaspoon vanilla
3 cups flour
1/3 cup cornstarch
1 teaspoon salt
1 teaspoon baking soda
For the frosting:
3- 8 oz packages cream cheese
4 sticks butter
1 pound powdered sugar (about 4 cups)
1 1/2 teaspoon vanilla
1/2 pint blueberries
2 pints raspberries
Cake:
In a mixing bowl, mix butter and sugar together on high until light and fluffy, about a minute or so. Add eggs, two at a time. Mix after each addition. Add sour cream and vanilla.
In a separate bowl, whisk together flour, cornstarch, kosher salt and baking soda. Turn mixer to low and gradually add flour mixture to butter/sugar mixture, one scoop at a time. Mix after every addition. Keep adding the flour mixture, mix until just combined. Do not overmix!
Grease and flour a 17 x 12 1/2-inch sheet cake pan.
Pour the thick cake batter into the pan. (It’s much thicker than regular cake batters.) With a knife or offset spatula, spread the cake batter evenly over the pan.
Place the pan into a preheated 350-degree oven and bake for 20 to 30 minutes, until a toothpick comes out clean. I baked mine for exactly 20 minutes, so you probably want to start checking then.
To make the cream cheese frosting, in a mixing bowl, add softened cream cheese and butter. Whip to combine. Add powdered sugar and vanilla. Mix until thoroughly combined, scraping the sides once during mixing.
Put about 1/2 the frosting on the cake. Mark off the area of the stars with a toothpick. Prepare a pastry bag with a large star tip and fill up to 2/3 with icing. Fold down both corners to keep icing from splurging out the top.
Gripping the folded-down end tightly under fingertips and start squeezing two lines of frosting at the bottom of the cake. Make two rows of raspberries on the cake, then add another two lines of frosting.
Keep repeating: two lines of frosting, two lines of raspberries, two lines of frosting, etc.
Fill the square in the corner with a nice layer of blueberries. With the star tip, squeeze little dollops of frosting all over the blueberries.
In a mixing bowl, mix butter and sugar together on high until light and fluffy, about a minute or so. Add eggs, two at a time. Mix after each addition. Add sour cream and vanilla.
In a separate bowl, whisk together flour, cornstarch, kosher salt and baking soda. Turn mixer to low and gradually add flour mixture to butter/sugar mixture, one scoop at a time. Mix after every addition. Keep adding the flour mixture, mix until just combined. Do not overmix!
Grease and flour a 17 x 12 1/2-inch sheet cake pan.
Pour the thick cake batter into the pan. (It’s much thicker than regular cake batters.) With a knife or offset spatula, spread the cake batter evenly over the pan.
Place the pan into a preheated 350-degree oven and bake for 20 to 30 minutes, until a toothpick comes out clean. I baked mine for exactly 20 minutes, so you probably want to start checking then.
To make the cream cheese frosting, in a mixing bowl, add softened cream cheese and butter. Whip to combine. Add powdered sugar and vanilla. Mix until thoroughly combined, scraping the sides once during mixing.
Put about 1/2 the frosting on the cake. Mark off the area of the stars with a toothpick. Prepare a pastry bag with a large star tip and fill up to 2/3 with icing. Fold down both corners to keep icing from splurging out the top.
Gripping the folded-down end tightly under fingertips and start squeezing two lines of frosting at the bottom of the cake. Make two rows of raspberries on the cake, then add another two lines of frosting.
Keep repeating: two lines of frosting, two lines of raspberries, two lines of frosting, etc.
Fill the square in the corner with a nice layer of blueberries. With the star tip, squeeze little dollops of frosting all over the blueberries.