The classic French 75 has the addition of simple syrup. I have made a similar rendition, minus the syrup. The French 74 is a cleaner cocktail with no sugar and fewer calories. 
Yield 1 cocktail
1½ oz. gin
½ oz. lemon juice
Top with cold champagne
Lemon zest for garnish
In a shaker, add the gin and the lemon juice and stir. Pour the mixture into a champagne flute or glass and top with champagne.  
Garnish with a small zest of lemon. 
Cheers, and enjoy!