To get this achievement right click the game, then click console, then type this: Game.cookies = 9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999
Then spam click grandmas to sell them. But then you must delete your save because you have beat the game and it doesnt work. To click this much i use OP.autoclicker3.0
I have also unlocked every achievement in game using this one command. It took about 5 to 10 minutes. Sadly, this command is not on mobile :(