In a mixing bowl cream together butter, shortening, peanut butter, 1/2 cup granulated sugar, and brown sugar until light and fluffy, about 2 minutes.
Add and eggs, mixing after each addition. Mix in the vanilla.
In a separate bowl whisk together flour, baking soda, and salt.
Stir dry ingredients into the wet ingredients and mix gently to combine. Don't over-mix. The dough will be very soft.
Pour remaining 1/2 cup of granulated sugar into a small bowl. Line a cookie sheet with parchment paper.
Scoop dough into balls and then roll in sugar.
Bake for 7-10 minutes, just until set. They will be pale, and look just barely set. Don't over-bake them or they will be hard once cooled.
Remove from oven and allow to cool on baking sheet for 2-3 minutes, and then transfer to cooling rack.
Press an unwrapped Reese's heart to the center of each warm cookie. Allow cookies to cool completely.
MAKE AHEAD, STORING AND FREEZING INSTRUCTIONS:To make ahead: These cookies will taste great made one day ahead of time or you could make the dough and store it in the refrigerator for 1-2 days before rolling in sugar and baking.To store: Store cookies at room temperature in a sealed container or bag.To freeze: Place cookies (once they have cooled completely) in a freezer safe bag in the freezer for 2-3 months.