A decoction mashed is used to get a solid malt character without using any crystal or other body-building malts. I suppose you could skip this if you wanted to substitute in a pound of carapils for Pilsner malt. But what fun is that?
Mash in at 122ºF and hold for twenty minutes.
Remove 1/3 of the mash from the thickest part of the mash. Bring to 158ºF and hold for ten minutes. Bring to a boil for five minutes and return to mash.
That should get you at about 150ºF. Hold for thirty minutes. Remove 1/3 of mash, heat to 158ºF, hold for ten minutes, boil for five minutes and return to mash.
Now you should be around or a little under 160ºF. Hold for thirty minutes. Remove 1/4 of the the mash and bring to a boil. Return to mash to hit mash out temp of about 170ºF. Hold for ten minutes and sparge.
Make sure to always stir your mash while heating to prevent burning and pull your decoctions from the thickest part of the mash.
Carbonate with 3/4 cup corn sugar for a proper sparkling mouthfeel.
Have fun and enjoy!