Preheat your oven to 350°F. Line a rimmed sheet pan with foil.
In a large bowl, whisk the egg, salt, pepper, garlic powder, onion powder, and thyme.
Add the ground beef, almond flour, and Parmesan. Gently mix, just until uniform.
Shape the mixture into a rectangular loaf by packing it into a plastic wrap-lined small loaf pan (8 X 4 inches).
Transfer it to the prepared baking sheet.
Brush the meatloaf with ketchup.
Bake the meatloaf until its center registers 160°F, 50-60 minutes.
Rest the meatloaf for 15 minutes before slicing and serving.
Video
Notes
Handle the mixture lightly. One of the most important things you can do to keep your keto meatloaf tender and fluffy is to handle it lightly. Mix just until everything is incorporated, and when you shape it into a loaf, be gentle.
Don't go too lean. I use lean (85/15) ground beef. This is the leanest you should go.
Don't use a loaf pan. It's best to bake a meatloaf on a large, rimmed baking sheetso the outside can crisp up. If you bake it in a loaf pan, it will bake inside its own juices and won't crisp up.
Foil is better. I tried making this recipe with a foil-lined pan and a parchment-lined pan. The meatloaf turns out much better when the pan is lined with foil, likely due to better heat distribution.
Let it rest. Rest the meatloaf for about 15 minutes before slicing it. This will help the juices redistribute and settle. It's never a good idea to cut into a meatloaf as soon as it emerges from the oven.
Leftovers: This meatloaf is one of those dishes that gets better the next day. You can keep it in the fridge, in an airtight container, for up to four days. Reheat the leftovers covered in the microwave, or - even better - slice and pan-fry the slices in olive oil. You can also serve them cold.