Add the flaxseed meal, sesame seeds (if using), and salt into a mixing bowl. Stir to combine. Add the water and stir again. The flaxseed meal and water will begin to form a dough. The longer you let the flaxseed "dough" rest, the drier it will get.
Place the dough onto two pieces of parchment paper, and use a rolling pin to roll it out as evenly as possible. If the dough is really sticky (it will always be slightly sticky), sprinkle extra flaxseed to slightly dry it out and make it easy to roll. The thinner you roll out the dough, the crispier the crackers will be.
Remove the top layer of parchment paper. Using a knife or a pizza cutter, score the dough into shapes (squares, rectangles, triangles ...). I usually cut the crackers into 40 (4"x 4") squares.
Bake the crackers at 350°F/(180°C for 20-25 minutes, or until crispy and golden brown. I recommend checking the crackers every 5 minutes after the first 15 minutes of baking. (If your crackers are thinner then mine, they will bake faster). If you find that most of the crackers are cooked through but a few right in the center are a little soft, you can just bake those few again for ~5 minutes until they've dried out more.
Allow to cool for 10 minutes and then break the "cracker" along the scored lines.
Store the crackers in an air-tight container for up to 3 weeks.
*I used golden flaxseeds because they have a more subtle flavor and lighter color than brown flaxseeds.