Add 1 1/2-inches of water to a baking dish and place it on the bottom rack of your oven. Place a rimmed baking sheet on the center rack. Preheat the oven to 400 degrees F (205 degrees C).
In a large bowl, use a fork to mix together the Water (1/4 cup) with the Unsalted Butter (2 tablespoon) and Fine Sea Salt (1/4 teaspoon) until combined.
Add the Parmigiano-Reggiano (1/2 cup) and continue to mix until it is thick and creamy. Stir in the Baking Powder (1/4 teaspoon).
Add the Einkorn Flour (1 1/4 cup) and continue to mix with a fork as much as you can, then use your hands to knead the dough in the bowl until it holds together.
Rub the dough against the sides of the bowl to collect any remaining flour, then turn it out onto your work surface and knead by hand about 20 times until smooth. Divide the dough into 5 equal pieces, and cover with plastic wrap to keep moist.
Cut a piece of parchment paper to fit your baking sheet. Roll out the first piece of dough as thin as possible on the paper, lifting frequently, until you have a 10-inch round. Sprinkle the surface lightly with salt.
Cut out the crackers with a 2-inch round cookie cutter as closely as possible. Pull up the outline of the dough, leaving the round cutouts on the paper. Slide the paper onto the preheated baking sheet.
Bake for 7 to 9 minutes until the crackers are lightly golden. Remove the pan from the oven and lift up the paper to gently shake the crackers into a large serving bowl to cool. Return the tray to the oven to warm up, then proceed to roll, season, and bake the remaining pieces of dough in the same manner.
Serve as is or with a dip of your choice. The crackers can be stored at room temperature in an airtight container for up to 3 days.