In a medium size bowl, using a mixer, cream together the butter and sugars. Then add the milk and vanilla.
Add the flour and salt and pulse on low. Do not over mix. If the dough is too sticky, add an extra 1/2 Tablespoon flour. If it's too dry, add an extra 1/2 Tablespoon of milk. Once the dough is your desired consistency, stir in about 1/3-1/2 cup of desired mix-in's.
If you'd like to roll the cookie dough into balls, refrigerate the dough for 30 minutes first. Then use a small cookie scoop and roll into 12 balls.
Store in an airtight container for up to 3 days.
Tip: If you are worried about using raw flour, you can heat treat the flour to kill any bacteria before using. Simply place the flour in a microwave safe bowl. Then microwave in 30 second increments and stir in between until the flour reaches 165°F. Let the flour cool before using.