Preheat the oven to 350 degrees. Lightly butter a cookie sheet, or alternatively, line the sheet with a strip of parchment paper. Set aside.
In a mixing bowl, mix together the flour, cocoa powder and baking soda. Set aside.
Using an electric mixer or a hand-held beater, cream the butter and sugars until the mixture is light and fluffy. Add the eggs and continue to beat until they are well-combined, about 1 minute. Mix in the flour, cocoa powder and baking soda mixture until well incorporated. Fold in the white chocolate chunks with a rubber spatula.
Filling a tablespoon, scoop out individual cookies from the batter and place in even rows on the cookie sheet, leaving 2 inches of space between each cookie.
Transfer the cookie sheet to the middle shelf of the oven, and bake for 8-10 minutes until the cookies are puffed and still to the touch. Remove the cookie sheet from the oven and allow cookies to cool and set for 5-7 minutes before carefully removing them with a spatula. If you have used a sheet of parchment paper, slide the entire sheet off the tray, and allow the cookies to cool for 5-7 minutes. Meanwhile, you may re-use the cookie sheet immediately for baking the next batch.