White chocolate: make sure to use real white chocolate. Most white chocolate chips you see at the store are not actually real white chocolate. Go for the white chocolate baking bars if purchasing at the store, or buy white chocolate callets online by brands such as Callebaut. To be considered white chocolate, it needs to have at least 20% cocoa butter. The white chocolate chips bought at most grocery stores won’t melt properly, they will most likely curdle as you try to heat and melt them.
Ad-ins: feel free to add chocolate chips or peanut butter chips to the brownie batter, or even nuts. Go for about 1/3 cup.
Alternative butters: Try making these brownies with a different butter, say almond or sunflower seed butter instead of peanut.