Preheat oven to 350 degrees F. Prepare a baking sheet with parchment paper.
In a bowl, whisk together the flour, cornstarch, baking soda and the baking powder. Set aside.
In the bowl of a mixer, combine the butter and sugar. Beat just until fluffy.
Mix in the eggs one at a time. Add 1/3 of the flour mixture and mix just until combined.
Add in ½ of the sour cream and mix until combined. Repeat with the flour and the sour cream once more, then end by mixing in last 1/3 of the flour mixture and mix just until combined.
Pour the cake batter into the prepared baking sheet and spread evenly. Bake for about 20 minutes.
Remove the cake from the oven, cool completely and then cut into rounds using a cup or cookie cutter sized for the jars you will be using.
Strawberries:
In a bowl, mix together the strawberries and the sugar.
Add the lemon juice. Mix well and let sit for about 20 minutes.
To Assemble:
Make the whipping cream with a mixer.
Layer the cake rounds with cake, whipped cream and strawberries into cups or jars. Layer until full to top.