In a large mixing bowl whisk together flour, cornstarch, baking powder baking soda and salt for 20 seconds, set aside.
In the bowl of an electric stand mixer fitted with the paddle attachment cream together butter and sugar until blended. Mix in egg then blend in sour cream, vanilla extract and almond extract.
With mixer set on low speed slowly add in flour mixture and mix until combined.
Divide dough into 2 fairly equal portions. Place each portion on a sheet of plastic wrap and shape each into a round disk about 6-inches.
Wrap with plastic wrap and chill 1 1/2 - 2 hours until fairly firm for rolling. Preheat oven to 350 degrees during last 20 minutes of chilling.
Dust a work surface with a fair amount of flour. Remove one portion of dough from refrigerator, remove from plastic wrap and transfer to floured surface.
Dust top with flour, then using a rolling pin, roll out to a 1/4-inch thickness. Cut into rounds (about 2 3/4 inch) or hearts.
Transfer to an 18 by 13-inch baking sheet lined with parchment paper. Gather scraps (shake excess flour off) and press together then re-roll dough and cut into shapes.
Bake in preheated oven for 9 - 11 minutes until cookies are nearly set***.
Let cool several minutes on baking sheet then transfer to a wire rack to cool (after about 5 minutes of cooling on a wire rack I transfer to an airtight container to finish cooling to seal in moisture). Repeat process with remaining dough in refrigerator.
Once cookies are cool frost with the vanilla frosting and store in an airtight container in a single layer.
For the frosting: In the bowl of an electric stand mixer (or in a mixing bowl using an electric hand mixer) blend together butter, powdered sugar, half and half and vanilla until well combined and fluffy.
Add in a little more half and half as needed 1 tsp at a time to thin. Keep covered until ready to use.
*To measure flour scoop flour with a measuring cup and sweep top using a butter knife. If you are in high humidity you may need to fold in a couple more tablespoons of flour at the end if the dough is super sticky.
**If there is a pool of liquid (whey) on top of the sour cream be sure to stir the sour cream well or even drain off the liquid before measuring.
***Be careful not to over-bake or they can be dry, but don't under-bake or they can be doughy and won't be as fluffy.
Note that this dough does puff up so I don't recommend using detailed cookie cutters.