What makes sugar cookies Puffy and Soft? (With premix sugar cookie)?

It sounds like they have dried out on you or you have cut them to thin. Reroll them thicker, if that doesn't help....

Try this: Add a couple of teaspoons of a fat such as room temp butter or solid shortening. If that doesn't help, it could be your mix is old or it is not the kind that produces the kind of cookie you are looking for. If you want to try to make your own that I promise you will turn out the way you want them, try this recipe. I have been making it for 20 years and when baked on parchment paper, they come out soft and thick and YUM!

Ingredients:

1 1/2 cups butter, softened

2 cups white sugar

4 eggs

1 teaspoon vanilla extract

5 cups all-purpose flour

2 teaspoons baking powder

1 teaspoon salt

1. In a large bowl, cream together butter and sugar until smooth. Beat in eggs and vanilla. Stir in the flour, baking powder, and salt. Cover, and chill dough for at least one hour (or overnight).

2. Preheat oven to 400 degrees F. Roll out dough on floured surface 1/4 to 1/2 inch thick. Cut into shapes with any cookie cutter. Place cookies 1 inch apart on ungreased cookie sheets.

3. Bake 6 to 8 minutes in preheated oven. Cool completely.

The ratio of brown sugar to white sugar will make a change in the softness of the cookie. More brown sugar will influence in a softer cookie. Extra white, less attackable crisper cookie. The shortening or butter you use will make a change also. Butter will give you a crisper cookie. Margarine or shortening provides you with a softer cookie. Alton Brown did an excellent show on this very subject. I have no idea when you can be competent to get all of the information but examine out the food network.

you might want to try keeping to the same butter or margarine, and add a bit more and some sugar and flour is necessary