For the cupcakes: Line two muffin pans with 18 cupcake liners. Preheat the oven to 350 degrees F.
In a large bowl or stand mixer, add 1/2 cup butter. Use the paddle attachment to beat it until smooth. If it's cold butter this will take a minute; remember to scrape the sides.
Add in 1/2 cup granulated sugar and 1/2 cup packed brown sugar. Beat into the butter for at least 90 seconds, stopping halfway to scrape the sides and edges of the bowl.
Add 1/4 cup oil. Any vegetable oil will do, I like to use light flavored olive oil. Too bad it's not also light in calories :) Oil makes our cupcakes really moist.
Add in 2 eggs and 4 teaspoons vanilla. Beat well and scrape sides.
Add 1/2 cup sour cream and beat well.
Use a strainer to sift in 1 and 1/2 cups all purpose flour, making sure to measure the flour by spooning it into the measuring cup and leveling it off. Add 1/2 teaspoon kosher salt and 1 and 1/2 teaspoons baking powder. Beat together, scraping down the sides of the bowl. Continue beating for another 60 seconds or so.
Add 1 cup mini chocolate chips and stir.
Use a scoop to fill 18 cupcake liners with the cupcake batter. You don't want to overfill them. Use about 3-4 tablespoons of batter per cupcake.
Bake the pans one at a time in the center of the oven for about 16-20 minutes, until a toothpick inserted in the center comes out with no wet batter on it. The edges of each cupcake should be firm to the touch. They should not brown on top. You can bake both pans at once if you have a nice oven that you trust, and if you rotate the pans halfway through the bake time. (My oven is an absolute joke so I always bake one pan at a time!)
With the help of a butter knife, remove the cupcakes from the pan within 1-2 minutes after coming out of the oven so the bottoms don't get soggy. Let rest on a wire rack until completely cooled.
For the frosting: Meanwhile, add 1 cup butter to a large bowl or stand mixer (clean it first). Beat well until smooth, scraping the edges.
Add 1 cup packed brown sugar and beat well, scraping the sides of the bowl.
Add 1 cup powdered sugar, 4 teaspoons vanilla, and 5 tablespoons milk. Beat well.
Add 1 cup of all purpose flour and 3/4 teaspoon kosher salt. If you are nervous about eating raw flour, first add the flour by itself to a bowl and microwave in 30 second increments until it reaches 160 degrees F. (I never do this. I live for danger. As my brother Nathan always says, "Look good, have fun, safety 3rd.")
Mix the flour in. When you can still see white streaks, stop the mixer and add 1 cup mini chocolate chips. Continue beating, scraping the edges, until it has all come together. Add more milk or flour as necessary to reach the consistency you like. Remember this is frosting, so you want it to be sticky; about the consistency of buttercream frosting.
Frost the cupcakes:Fit a wide-mouthed frosting tip (like tip size 1A is perfect) into a pastry bag, or the corner of a ziplock bag that has had the end snipped. Set the bag into a tall empty glass to brace it. Use a spatula to add the cookie dough frosting to the bag. Pipe the frosting in a swirl on top of each cupcake.If you don't want to pipe, use an offset spatula to spread frosting on each cupcake.Top with mini or semi sweet chocolate chips! Devour with milk!
Store these covered on the counter up to 3 days. After that, stick them in the fridge.