Preheat oven at 350F/180C. I've actually had better results baking in a 375F/190C oven, but this depends on your individual oven. Investing in an oven thermometer also helps make sure your oven temperature is where you want it.

Prepare two 12 cup muffin tins with paper liners or grease the tins themselves. Metal muffin tins and silicone baking cups/pans do conduct heat differently so if you want to use silicone, play around with the temperatures and times (probably a lower temp for a bit longer)

Mix the butter with either a hand or stand mixer until soft. Add the sugar at once and cream for 5 minutes on a high speed or until light and fluffy. Make sure to scrape the bowl. You want a fluffy texture to this mix, but you don't want the butter so soft that it breaks down. It should look similar to cookie dough.

Add eggs, egg yolks, and oil one at a time, combining well after each one. I like putting the eggs in a separate bowl since you can check for blood spots or bad eggs and eggs separate better cold. Also make sure to mix the eggs and oil in very well and scrape the bowl down frequently. At this point it will look more like cake batter.

In a separate bowl, mix the flour, cornstarch if using, salt, baking powder, and baking soda. Sift or use a whisk to combine very well.

At this time, I also add my extract with the milk mix. Add a third of the flour mix into the butter mix and gently combine just until the flour is incorporated. Add half the milk mix and gently combine again until the milk is incorporated. Scrape down the bowl very well. Repeat this with another third of the flour and the last half of the milk. Add in the last third of flour and mix just until you no longer see any flour. It's important once you add the flour that you don't overmix!!

Fill up the cups 2/3 full. The easiest is to use an ice cream scoop since you want all the cupcakes filled evenly. You also don't want to leave the batter out for too long since the baking soda and baking powder will begin reacting once it's mixed with liquid (most baking powders will react twice: once with liquid and once with heat), but this will affect the texture and appearance.

Place in the middle rack of the oven and bake for 15-18 minutes. I'll bake at 375F/190C for 10 minutes and then drop the heat to 350F/180C for the last 5-8 minutes. Don't open the oven door for 15 minutes! Cupcakes will be done when a few moist crumbs attach to a toothpick inserted, they spring back lightly when touched, and they no longer look wet. If a toothpick comes out clean, I find the cupcake is overcooked and will taste dry.

Let cool completely on a wire rack. Frost with your favorite frosting and enjoy! I also tried to add as many baking tips as I could, but the biggest tip is learning how your own oven heats up and functions. Buy an oven thermometer!

They store at room temp for a day or two, but you can freeze them unfrosted if you're planning on serving later. Just let them thaw for a few hours and they're ready to go.