Preheat oven to 300°F
In a mixing bowl with a whisk, whip your eggs and sugars together until light and airy about 5 minutes. You should be able to see little air bubbles in the mixture.
Add in the melted butter, oil, espresso powder or instant coffee, and vanilla and mix to combine.
Next, sift into the bowl the cocoa powder, flour, and salt. mix until just combined, don't overmix the batter.
Grease an 8x8 baking dish with a little bit of butter or cooking spray. Put the mixture into your greased dish and bake for 50 minutes.
Pull your brownies out after 50 minutes and scoop the peanut butter in several little bits over the top. I usually separate it into 5 scoops. Place back in the oven for an additional 5 minutes.
Pull your brownies out, the peanut butter should be nice and melty, spread the peanut butter evenly over the top of the brownies and sprinkle with flaky salt while it is still hot.
Allow to cool for at least an hour before cutting in, I know its hard but it will be brownie soup if you don't wait.
Cut into 12 pieces and enjoy!