Preheat the oven to 400 degrees Fahrenheit.
Prepare the mashed cauliflower according to package instructions. When it's done, stir in the cheddar and parmesan cheese until they melt, then set it aside to work on the dough.
Add the mozzarella and cream cheese to a large microwave-safe bowl. Microwave for 30 seconds, stir, and then microwave for another 30 seconds. Stir again. At this point the mozzarella should be fully melted into a gooey, stretchy ball with the cream cheese fully melted into it. If not, give it another 10-15 seconds in the microwave. Add the egg, almond flour, and salt, and using a spoon or oiled hands, mix together into a uniform yellow ball.
Place the dough onto a long piece of parchment paper and top with another piece of parchment. Roll the dough out to 1/8-inch thickness, then cut out 4" circles with a cookie cutter. Place the circles on a parchment-lined cookie sheet, then roll the scraps up into a ball, roll it out again, and repeat cutting the circles until you have 12.
Dollop the filling by scant tablespoonfuls into the center of each circle, then fold them over and crimp the edges with the oiled tines of a fork to seal. You will use about 1/2 of the prepared filling. If you choose to double the recipe, make a second batch of dough after you've sealed the first batch of pierogies, so the dough doesn't cool and lose its pliability.
Make sure the prepared pierogies are at least 2" apart on the cookie sheet, and bake for 12-14 minutes, until golden brown.
Macros per serving will be an overestimate as there will still be scraps of fathead dough left over. 347 calories, 5 grams net carbs, 21 grams protein, 26 grams fat.