Step 1

Preheat the oven to 350°

Step 2

In the bowl of a mixer cream the butter with both sugars until smooth.

Step 3

Mix the oil and eggs until combined.

Step 4

Next mix in the cornstarch, baking soda, cream of tartar, salt, cocoa, and flour and mix until it's all well incorporated.

Step 5

Use a 2 tablespoon cookie scoop and place the cookie dough onto parchment lined baking sheets.

Step 6

Bake for 10 minutes. You can test with a toothpick, a toothpick should come out clean.

Step 7

Glass Bottom method-use and antique glass with a decorative bottom or a smooth measuring cup.

Step 8

While the cookies are still warm, about 2 minutes out of the oven...

Step 9

Add a little dab of butter or frosting to the bottom of the item you will be adding sugar too.

Step 10

I used a measuring cup, then added a dab of butter to it and dipped the smooth bottom of the measuring cup into granulated sugar.

Step 11

While the cookies are still warm, gently press the bottom of the measuring cup onto the cookies, the edges of the cookies may crack a bit, that is ok, don't squish the cookies or press too hard.

Step 12

Allow the cookies to cool completely.

Step 13

Spread frosting onto cookie with a small offset spatula. Allow frosting to set up completely so it won't get messed up if you move them or stack them. I allow the frosting to set up for a few hours to overnight if I'm going to stack them.

Step 14

In a large bowl of a mixer beat butter until smooth, add in powdered sugar and cocoa.

Step 15

Pour in melted chocolate and add heavy cream and vanilla and beat on medium-high until it's all creamy and smooth.

Step 16

Spread frosting onto cookies with a small offset spatula, start by applying the frosting into the center and as you press down in the center swirl the spatula around in a circle to create a pretty swirl shape of frosting on the cookies.