In a bowl whisk together the all-purpose flour, rye flour, cornmeal, poppy seeds and baking powder.
Use your fingers or a pastry blender to mix in the cold butter pieces until the mixture resembles crumbs.
Stir in the Parmesan and cheddar cheeses until they are evenly distributed.
Sprinkle 4 tablespoons of water over the mixture while stirring until everything is well combined. If it seems dry add a tablespoon of water.
Transfer the dough onto a surface. Knead it gently. Divide it into two portions shape each portion into a disk shape wrap them in plastic wrap and refrigerate for one hour.
Set your temperature to 400°F (200°C).
On a floured surface roll out one disk at a time to 1/8 inch thickness. Cut out shapes using cookie cutters or alternatively slice them into squares. Place them on a baking sheet lined with parchment paper.
Whisk an egg with 1 tablespoon of water and brush this mixture over each cracker. Sprinkle some sea salt on top for added flavor.
Bake for around 12 to 15 minutes. Until they turn brown.
For an added touch of crispiness, you can keep them in the oven after it's turned off for a few minutes.
Allow the crackers to cool down before placing them in a sealed container, for storage.
Now you can savor your delicious homemade Parmesan Cheddar Crackers with a sprinkle of Poppy Seeds!