Champagne and Prosecco, two fantastic ‘bollicine’, but please, do NOT compare the two! Just because both happen to be sparkling whites, doesn’t mean they are similar. Would you compare a Barolo to a Pinot Noir just because they are both reds? No! You just don’t do it.
First they are made from two different grapes. Prosecco from the semi aromatic prosecco grape, grown in the hills of Conegliano-Valdobbiadene (an area about 45 min north of Venice), and Champagne, grown in, well Champagne, and is either made completely from chardonnay grapes (as in the blanc de blancs) or a mix of chardonnay, pinot noir and pinot meunier. Next, they are made in two different modes. Champage is a classic, and probably one of the oldest sparkling wines. The method, called Champenoise, or just classic method, has been carried down by generations, and it is no easy process. First it follows the normal fermentation process and creates a so-so dry wine. Next, the wine is bottled, then sugars and yeasts are added (called liqueur de tirage) to start a second 
fermentation. The bottles are capped and placed in a pupitre. This is an upside down ‘V’ shaped piece of furniture which has holes cut into it to support the champagne bottles. The bottles are places horrizontaly into the lowest level (closest to the floor) and every so often they are moved up the pupitre until they reach the top and are almost vertical. At this point, the fermentation has finished and what is left other than the carbon dioxide (aka bubbles) is a thin film of dead yeast cells sitting at the top of the bottle. The neck of the bottle is then frozen, uncapped and the dead yeast comes shooting out (degorgement). Before the bottle is recapped sometimes extra sugar is added (liqueur d’expedition) therefor giving champagne its character ex. brut, dry, extra dry. The bottles are then allowed to sit for a bit then shipped off to your local restaurant.
The process called Charmat or Martinotti, which is what is used to make prosseco, is quite simple, and one of the
reasons it costs much less! After it is made into a still wine, it is moved into huge steel vats which are sealed tight. Yeasts and sugars are added, and the pressure in the vat is turned up. This causes a second fermentation and in the end, bubbles. After a short while, you have sparkling prosecco, ready to be bottled. So short in fact the the bottles must be commercialized within 6 months after the making. The pressure inside the bottle is much less then that of Champagne, only 3 atm (atmosphere) whereas the latter has 6 atm, therefor the bubbles are less, lighter and somewhat bigger in size.
In the end both styles are great and create 2 highly enjoyable but different wines. If your looking for an Italian Champagne, try a Franciacorta or Cruase… at least the grapes and processes are the same!