Firstly make the egg replacement, by placing the oats in a small heat-proof bowl or jug and covering them with the boiling water. Stir briefly to combine, and then set aside until thickened and cooled.
In a large bowl add the almond butter, plant butter and both sugars and mix together by hand with a silicone spatula or wooden spoon, until well combined. Then add the cooled oat mixture and mix again until just combined. Finally, add the flour & salt to the mixture, and mix together until a soft dough forms.
Lightly flour your work surface, and using a rolling pin, roll the dough out until a few millimetres thick. Then using a cookie cutter of your choice, cut out 17 cookies - you may need to re-roll the dough once or twice to be able to cut all the cookies out. Place the cookie dough shapes onto lined baking trays, and place into the fridge to chill for 30 minutes. Meanwhile, preheat your oven to 175C/155C Fan/Gas Mark 4.
Once the cookie dough shapes are chilled and firm to the touch, bake for 15-17 minutes in the oven until lightly golden brown. Leave to cool on the tray for a couple of minutes, before placing them on a cooling rack to cool completely.
Cookies can be kept in an air-tight container at room temperature for 1-2 weeks.