1 HOUR IN ADVANCE: Set out the butter, cream cheese, and egg to get to room temperature. Make sure these ingredients are all at room temperature before starting. Don't melt any of these ingredients in the microwave or the texture will be off. (See Note 2)
CREAM BUTTER AND SUGAR: In a large bowl, cream together the sugar and butter with an electric hand mixer until light and fluffy. (Alternatively, cream together in a stand mixer).
REMAINING WET INGREDIENTS: Add in the cream cheese and continue to beat until the batter is completely smooth. Beat in the egg, vanilla extract, lemon extract, lemon juice, and lemon zest. When zesting the lemon, be careful to avoid the white part of the lemon; this is called the pith and is very bitter; just get the very outside yellow part.
DRY INGREDIENTS: In a separate bowl, combine the flour, baking powder, salt, cornstarch, and pudding mix. Stir together and then add to the wet ingredients. Mix until just combined, being careful to not over-mix (to avoid dense cookies).
CHILL: Cover the dough tightly and chill for 45 minutes.
MEASURE COOKIE DOUGH BALLS: Preheat the oven to 350 degrees F. Using a 1 tablespoon measuring spoon, measure in the cookie dough to just fill up the measuring spoon (not heaping; these are small cookie balls). Place cookies 2 inches apart on a parchment or Silpat- lined baking sheet. I bake 8-10 at a time.
BAKE: Bake at 350 degrees F for 9-11 minutes (10 minutes is perfect in my oven) and then remove from the oven. Remove to a cooling rack and let cool completely. Be very careful to not over-bake these cookies as they go from a thick soft cheesecake texture to a biscuit-like texture very quickly.
GLAZE: Once cooled, prepare the glaze by whisking together the lemon juice and powdered sugar. Add the lemon juice just until a thick glaze can come together. Spoon the glaze over the cookies and allow to set.
STORAGE: Store cookies in an airtight container in the fridge for 3-5 days. These cookies don't freeze or thaw very well.