Preheat oven to 350 degrees F. Line an 8 inch pan with nonstick foil or parchment.
Chop the candy bars, then put them in a food processor (or mini processor) and grind them.. 6 bars should give you 3/4 cup. You can also use a chef's knife and just chop the cold bars into tiny bits.
Beat the very soft butter and the sugar together in a large bowl until blended.
Beat in the egg, water, and vanilla. Add the salt and baking powder and stir until blended, then add the cocoa powder and stir until blended.
Add the flour and stir until blended, then fold in your ground up candy bars.
Scrape the batter into the prepared pan. Bake for about 30 minutes (I usually pull them at 28) until the center is set, the edges look a bit crusty, and the top of the brownies start to crack a little.
At this point you can take the optional step of slicing more Snickers bars and laying them on the hot brownies. Allow the brownies to cool, then put them in the refrigerator or freezer to chill. When very cold, cut into squares.