Line an 8x8 baking dish with parchment or wax paper.
Add the cream, cream of tartar, corn syrup, sugar and brown sugar to a 2 quart saucepan and heat over medium-low heat until the sugar dissolves.
Increase heat to medium, bring to a simmer and cook for 1 minute.
Remove from heat and stir in the vanilla, peanut butter and toffee chips.
Continue beating your mixture until it is very thick and difficult to mix.
Pour mixture into the pan and sprinkle with the sea salt.
Let set for about 1 hour, or until mostly cooled.
Cut the fudge into 1" pieces with a warmed knife.
Store the fudge in an airtight container in the refrigerator.
Be sure the sugar fully dissolves before bringing it to a simmer - if it's not dissolved your fudge could come out grainy;
After it's removed from the heat, make sure the fudge is beaten long enough to become very thick before pouring it into the pan;
Let it set fully before trying to slice it. You can cool it more quickly in the fridge. Using a warm knife helps to slice the fudge cleanly.
To save fudge that hasn't set, pour it back into a saucepan with about 1 cup of water. Heat over low heat, stirring until dissolved. Increase the heat to medium and bring to a simmer - cook for 1-2 minutes. Remove from heat and stir in another ¼ cup of peanut butter and beat until it has thickened. Pour back into the pan and let it set.
It will last in an airtight container at room temperature for about 2 weeks or it can be stored in the fridge for up to 4 weeks.
Individually wrap your pieces of fudge in parchment paper or plastic wrap. Place in layers inside a freezer bag and store for up to 3 months. Thaw at room temperature and enjoy!