Preheat oven to 375 F. Line the cupcake tin with papers.Sift the flour, cornstarch, baking powder and salt into a large bowl then whisk together and set aside. Add the butter and the mix of sugar and lemon zest to the bowl and mix until light and fluffy. Add one egg at the time and keep mixing.
Add half of the dry ingredients and mix on the low speed setting of your mixer until combined. Add the sour cream, milk, lemon juice, vanilla extract and mix again.Add the rest of the dry ingredients and give it a final whisk. When the cupcake batter was ready, I decided to add a few drops of yellow food coloring to enhance the color of the lemon cupcakes. Fill the cupcake papers about 3/4 of the way up. Bake for 18-22 minutes at 350F degrees.Check the readiness of the cupcakes with a skewer or a toothpick. Transfer the cupcakes on to a cooling rack and let them cool completely. To make the raspberry cream cheese frosting mix the butter and powdered sugar for a few minutes and add the cream cheese, mixing on the low speed of your mixer until everything is combined well.
Add the vanilla extract, raspberry jam and mix again. The raspberry cream cheese frosting is turning out very smooth, holds its shape well and has a very nice blush pink color.
To decorate my cupcakes, I used a large open star piping tip. I put the piping bag in a tall drinking glass and filled it with the cream cheese. I found this way to be the easiest way to transfer frosting to the piping bag.
Now all that you need to do is pipe your frosting into a simple swirl and decorate it with fresh raspberries and a little piece of lemon.
To take your cupcakes to the next level of goodness, using a large decorating tip, remove the center of the cupcake. The hole you create should be about a 1/2 inch to 3/4 inch deep. Fill each cupcake with approximately 1 teaspoon of raspberry jam. Cover the hole with the part of the cupcake that you took out and decorate with the frosting.