Directions

Place flour, 2 tablespoons dehydrated onions, dehydrated chives, sugar, baking powder, and salt in a food processor and pulse a few times to combine. Add the cold butter cubes and pulse until the butter is about the size of peas, about 6 to 8 times. Add the grated cheddar and gruyère and continue to pulse until the cheese is incorporated in the butter and flour mixture, then with the motor running slowly stream in 3 tablespoons ice water and pulse until the dough starts to form a ball (it’s okay if it’s a little shaggy).
Turn the dough onto a lightly floured surface, bring the dough together into a round with your hands, and knead a couple times. Roll the dough into a 12-inch round. Fold the top and bottom into the center so they meet in the middle, then repeat the same process with the sides, creating a square (this is creating lots of flaky layers!). Wrap in plastic wrap and chill for 45 minutes.
Preheat the oven to 350°F. Line two baking sheets with parchment paper and set aside.
Remove the dough from the refrigerator, divide in half, place one half on a lightly floured surface, and return the other half to the refrigerator.
Roll the dough out into a rectangle about 13x10” and no more than ⅛” thick. Using a fluted pastry cutter, trim the edges, saving the scrapes, to create a clean rectangle. Transfer the dough to one of the parchment-lined baking sheets. Cut the dough into 1½” strips lengthwise and 1½” strips crosswise to create square crackers. Using a fork, dock each cracker diagonally across the center (this will allow steam to escape when baking). 
Using a pastry brush, brush the top of the cut dough with a thin layer of heavy cream and sprinkle each cracker with a few flakes of flakey salt and then sprinkle 1½  tablespoons of dehydrated onions evenly over the top of the crackers. Pull the crackers apart so there is about ⅛” between each one. Freeze for 10 minutes. (At this point, the crackers can be frozen completely, and then transferred to a zip-top freezer bag to be baked later. The unbaked crackers are good in the freezer for up to 1 month.)
Bake the crackers, turning the tray halfway through, until they are slightly puffed and golden, about 16 to 20 minutes. If baking from frozen, the crackers might take a couple extra minutes.
While the first batch of crackers is chilling and baking, repeat the rolling and cutting process with the remaining half of the dough. Combine any leftover scraps into a ball, reroll, cut, and garnish that dough.
Cool the crackers for 15 minutes before serving and enjoy with bubbles or your favorite batch cocktail! Crackers can be kept in an airtight container for up to 2 days.