Preheat oven to 375°F. Line three baking sheets with parchment paper.
To a large bowl, add shortening. Pour in the melted butter and whisk until the shortening melts. (A few small lumps of shortening are okay.)
Add the brown sugar and vanilla, whisking to combine.
Mix in the eggs, one at a time, followed by the peanut butter.
One by one, add the baking soda, baking powder, and salt into the bowl. After adding each ingredient, whisk vigorously to ensure proper mixing.
Using a rubber spatula, fold in the flour until fully incorporated. The dough will be soft and sticky.
To a bowl, add the granulated sugar. Using a ¼ cup (or 2 scoops of dough with a 2 tablespoon scoop), set the dough onto a lined baking sheet, about 2 inches apart. (I usually put 6 cookie dough balls onto each cookie sheet.)
Roll each cookie into the sugar and place back onto the baking sheet.
Sprinkle each cookie with flaky sea salt and bake for 14 to 16 minutes, rotating the pan halfway through baking, until the tops are puffed and crinkly and the edges are golden brown.
Remove the cookies from the oven. Using a spatula, gently press down on each cookie to flatten.
Let the cookies rest for a few minutes before transferring to a wire rack to continue cooling. Enjoy them warm or cooled completely.