Pour 1 cup of peanut butter, the sweetened condensed milk, and sea salt into a large mixing bowl, and combine until the mixture is smooth.
Add the remaining peanut butter to a microwave-safe bowl and heat it for 1 minute in 15-second increments, stirring after every increment, until it is melted and smooth, then let the peanut butter cool slightly.
Meanwhile, pour the chilled heavy cream and vanilla bean into the bowl of a stand mixer equipped with the whip attachment. Whip the chilled heavy cream and vanilla extract on high until it is stiff. Fold the whipped heavy cream and vanilla mixture into the peanut butter and condensed milk mixture until fully combined.
Pour half of the peanut butter ice cream into a freezer-safe 8 by 4-inch or 9 by 5-inch loaf pan. Drizzle the ice cream with 1/4 cup of the cooled melted peanut butter, 2tablespoons of walnuts, and 2 tablespoons of toffee pieces. Add the remaining ice cream batter, drizzle with more of the melted peanut butter and use a butter knife to swirl the melted peanut butter into the ice cream.
Cover the ice cream tightly with plastic wrap before placing the cover on the loaf pan. Freeze the peanut butter ice cream for at least 6 hours or overnight before serving.
Top the ice cream with the remaining walnuts and toffee pieces before serving.