In a medium bowl, whisk together the cake flour, bread flour, baking soda and baking powder.
In a large bowl (you can use an electric stand mixer or use a handheld electric mixer), cream the butter until light and fluffy, 1-2 minutes.
Add granulated and brown sugar and salt. Mix well.
Add the eggs, vanilla and peanut butter, Mix until the batter is very light in color, 2-3 minutes.
Add the dry ingredients and mix until just incorporated.
By hand, mix in the chocolate and peanut butter cups. Cover the dough with plastic wrap and refrigerate for 2 hours or up to 24 hours.
Preheat the oven to 350 degrees F.
Line baking sheets with parchment or silpat liners. Form balls of dough with about 2-3 tablespoons of dough (each of my cookie dough balls weighed 2.55 ounces - how's that for fussy?).
Place on the cookie sheets about 2 inches apart. Sprinkle lightly with fleur de sel. Bake until the cookies are golden around the edges but still soft in the middle, 13-16 minutes. Keep the dough refrigerated in between batches.
Notes
A Little Fussy: these cookies are fussy, no doubt. The ingredients should be weighed, dough requires cake flour and bread flour and needs some chilling. But the results? Totally and completely worth it.