Preheat the oven to 350°F & grease and parchment line 4-7" cake pans (2-8" pans will also work)
Combine the flax meal with the warm water & set aside to thicken about 5 minutes.
Sift the baking powder with the flour set aside
Combine the vinegar & vanilla extract with the plant milk
With the paddle attachment on your electric mixer cream the room temperature vegan butter with the sugar on medium to high speed until fluffy about 3-5 minutes then add the peanut butter to blend well
Add the flax paste & whip on high speed to emulsify for 10 seconds
While mixing on low speed add about 1/3 of the flour mixture, mix just until it is incorporated then while still mixing on low speed slowly add in about half of the milk mixture
Quickly add another 1/3 of the flour mixing just until it is incorporated then add the rest of the milk mixture & finishing with the last addition of flour. This is called alternating creaming method & the entire process should not take more than 1 minute Divide evenly between the prepared pans & bake for approximately 25-30 minutes or when they are springy to the touch when you gently press the centers
For the Peanut Butter Fudge:Combine the peanut butter and agave or corn syrup in a heavy bottom sauce pot and bring to a boil stirring constantly. Boil for about 1 minute then add the coconut oil and vanilla extract and transfer to a bowl to cool
While the cakes are baking and/or cooling prepare the buttercream & ganache recipes
For the Peanut Brittle: Combine the sugar, corn syrup & water in a medium sized heavy sauce pot & bring to a boil stirring occasionally with a wooden spoon or a heat proof silicone spatula to dissolve the sugar but do not stir it after it comes to a boil .
Once it boils, Insert a candy thermometer & continue to boil without stirring until it is 300-309°F (*See notes above about my speaking error in the video) it should just start to turn golden brown, then add the vegan butter, baking soda, vanilla extract and peanuts, stirring well to combine
Spread mixture on a lightly oiled sheet pan or a silicone baking mat & let it cool completely then crack it up to jagged pieces
Assemble cake as shown in the video