Preheat the oven to 325℉ (163℃)
Line a 9" by 13" glass baking dish with parchment paper. Note 3 and Note 4
Melt the butter in a microwave safe bowl in 10 second increments.
In a large mixing bowl, add both the brown and white sugars and the melted butter. Beat with a hand mixer on medium-high for two minutes until fluffy and lighter in color.
Add the eggs one at a time, incorporating after each addition. Beat for another two to three minutes on medium.
In another bowl, sift together the flour, cocoa powder, baking powder, and salt.
With a spatula, fold the dry ingredients into the wet until thoroughly combined (make sure not to over mix.)
Chop the dark chocolate bar into rough chunks and set aside.
Chop the cherries (IF USING FROZEN, DO NOT LET THEM THAW FIRST). Note: Make sure when using frozen pitted cherries to chop them in half at least to make sure there are no pits.
Fold the chocolate chunks and cherries into the batter until just distributed.
Transfer the batter to glass baking dish.
Bake for 45-47 minutes until the center is slightly wobbly but the edges are firm
Note: Let the brownies cool fully before cutting.