Heat oven to 350°F
Line bread pan with parchment paper - use one sheet to cover the long sides and bottom, fold against the short sides of the pan
Rice cauliflower in food processor - even if you buy pre-riced you'll want to make it as fine as possible
Steam cauliflower in mircrowave until it is soft - you can also gently steam in a pot or pan on the stove, just make sure it doesn't start to brown
Allow cauliflower to cool a bit
While cauliflower is cooling, separate eggs
Place the whites into a mixing bowl or stand mixer bowl and set the yolds aside
Beat egg whites until stiff peaks form
Set beaten egg whites aside
When cauliflower is cool enough, place in a clean dish towel or mesh bag and squeeze out as much water as you can - there should be a fairly dry ball of the cooked cauliflower and it will be reduced in size by about half - 1 ½ cups or so left. Set strained cauliflower aside,
Add the egg yolks, almond flour, melted butter, olive oil, baking soda, apple cider vinegar and salt to large mixing bowl or stand mixer bowl
Beat for a beat at medium speed until everything is combined
Add the cauliflower
Beat at medium speed until the cauliflower is thoroughly mixed in
Carefully fold in a third of the whipped egg whites using a spatula. You want the batter to remain airy. Contiue adding the rest of the egg white, gently folding in until they are mixed with the batter. Don't stir them in, just incorporate so they are mixed with the batter, but still airy
Pour batter into parchment-paper-lined bread pan
Bake for 50 - 55 minutes until bread is firm on top in the middle of the loaf
Cool in pan on wire rack for 15 - 20 minutes
Lift loaf out the pan using the parchement paper and place the loaf on the wire rack
Cool completely before slicing
To store: Wrap loaf in paper towel and place in an air-tight bag or container. Store in refrigetor for up to a week. Freeze bread for up to three months - freezing tip - slice bread and place pieces of parchment paper between each slice before freezing.