I've been making these cookies for over 20 years. The recipe started from the Quaker Oats Oatmeal Raisin Cookie recipe, I tweaked it a bunch and came up with this.

I get asked a lot "how do you get them to be so big?" The answer is the fat-sugar-flour ratio and a large ice-cream scooper (mine is a #10 aka 3.25 oz.).

Try to use quality ingredients, especially on the butter, vanilla, flour and chocolate.

Make sure your butter is cold, straight from the fridge.

2 sticks of butter
2 cups of brown sugar
1/2 cup of white sugar
2 eggs
1 tbsp real vanilla (not imitation)
1 tsp salt
1 tsp of baking soda
1 tsp baking powder
3 tbsp old fashion molasses
3 cups of AP flour
3 cups of Old Fashion Oats (not quick oats)
3 cups of semi sweet chocolate chips

Cream together the butter and sugars
Add the eggs and mix
Add the vanilla and mix
Add the salt, baking soda, baking powder and mix
Add the molasses and mix
Add the flour and mix
Add the oats and mix
Add the chocolate chips and mix

Scoop balls on to a large (half pan) cookie sheet, 6 balls per sheet
Bake at 335 convection (or 350 regular) for 15 minutes

My batch (using my ice cream scoop) will make 3 cookie sheets (18 cookies total)
The top most sheet will be done first and the two sheets below will stay in the oven a minute or two longer.

I usually "eye-ball" the amount of molasses I use, but be careful, too much and it will over power the flavor.
Sometimes I use (add to the recipe) a baking emulsion to give another layer of flavor, the one I like is the Buttery Sweet Dough.