Grate or shred 1/2 stick of frozen butter and transfer it back to the freezer until time to add it to the batter
Dice the other 1/2 stick of butter into 1/4" cubes and transfer to the freezer.
Reduce speed to low and stir in the frozen butter shreds, cubes and the whole egg or yolk powder just until combined.
Spread the batter onto a large, parchment paper lined quarter sheet pan.
Bake in the preheated oven for 10 minutes.
Meanwhile, mix together the olive oil, rosemary and garlic in a small bowl.
Using a pastry brush, spread the olive oil mixture evenly over the top of the bread and sprinkle with flake salt.
Transfer the bread back to the oven and bake for an additional 25 minutes.
Allow to cool on the wire rack for about 10-15 minutes.
Slice into squares and enjoy!
Substitution options:
1 tsp of gelatin can be replaced with 1/4 tsp of xanthan gum.
Allulose can be reduced. If you eliminate it all together try increasing the oven temp to 375-400 degrees in order to get some browning on your loaf. Check for doneness before the whole 35 minutes are up.
Arrowroot can be reduced to 1 tbsp or eliminated for a lower carb count.