Firstly, mill the flour. I like to use spelt, but Einkorn or Soft wheat would also work. OR even a blend of any of those three.

Add the starch, baking soda, and salt to the flour and stir to combine. Set this dry mixture to the side while you work on the wet ingredients.

In a stand mixer, or using a hand beater, cream together the softened (not melted) butter, peanut butter, sugar, and brown sugar. Cream until light and fluffy, and it seems to increase in amount.

Add the vanilla extract and the egg to the creamed butter and sugar mixture, beat until combined.

Then, add the dry ingredients to the wet ingredients, and mix until combined and no dry flour is left.

Let the dough sit for 10 minutes or so for the fresh milled flour to start absorbing the moisture.

While the dough is resting, prepare your baking sheets with parchment paper.

Preheat the oven to 300*F.

Using an extra small cookie scoop, scoop out the dough balls onto the prepared cookie sheet. If you don't have a cookie scoop, this can get messy rolling them into balls with your hands, so you may want to chill the cookie dough if this is the case.

The cookie dough balls will spread and flatten in the oven while baking. so, make sure to leave plenty of room on the cookie sheet between each cookie dough ball.

Bake the cookies for 16-20 minutes. Once done, they should have flattened, and the edges will be golden brown. They will crisp up a bit as they cool.

Allow the cookies to cool on the pan completely while they crisp up. (They continue to bake a bit on the hot pan while cooling.) So, it is best to have more than one pan to alternate between baking and cooling.

While the cookies are cooling, then make the peanut butter filling.

To make the peanut butter filling, in a stand mixer, or a using a hand beater, place the softened butter and creamy peanut butter in the bowl. Then beat together.

Then, add the powdered sugar and beat until combined. It should be somewhat thick at this point.

To thin the filling, add in whole milk (or cream) a little at a time while beating in between. You are looking for a thick, creamy, spreadable consistency.

Put the filling into a piping bag, or you can spoon a little bit at a time onto the cooled cookies.

To assemble the sandwich cookies, place one cooled peanut butter cookie upside down, then pipe in the filling in one layer but not all the way to the edge of the cookie. A little bit goes a long way.

Then, place another cookie on top of the filling right side up and press lightly until the cream spreads to the edge of the cookie sandwich.

Repeat this process until all cookie sandwiches are made. If you used a 1 TBSP cookie scoop, these will be a bit larger like in my photos. These will bake closer to the longer bake time, and you should get about 48 single cookies to make 24 cookie sandwiches. But, if you use a smaller cookie scoop (which I recommend) Then, you will get more cookies and more sandwiches. The smaller cookies will bake closer to the lower bake time. However, everyone's oven is a bit different, so just check on them towards the end to see if they need more or less time.