Using a very sharp knife, slice the bread on a diagonal as thinly as possible (⅛-inch or less). Arrange on a parchment paper lined sheet pan. Using a pastry brush, brush melted butter on both sides of the bread slices. Sprinkle sea salt over the top of the bread. You will probably need at least two sheet pans as one baguette will make a ton of crisps
Bake at 350° for about 15 minutes, until the bread is nicely browned and crisp. Remove from the oven and cool on the baking sheet. Store in an airtight container at room temperature.