• In a small bowl, whisk the ground flaxseeds and lukewarm water. Set aside 10 minutes until a gooey and egg-like texture forms.
• In a non-stick saucepan, over low-medium heat, melt the butter.
• Str in the sugar and brown sugar and stir and cook for 1 minute or until the sugar melts.
• Remove from the heat and stir in the vanilla extract and flax egg.
• Transfer the mixture into a large bowl.
• Stir in the flour, salt, and baking powder until a thick, golden batter forms. The batter is slightly lukewarm, so don't stir the chocolate chips now, or they will melt.
• Refrigerate the batter for 10 minutes to slightly cool it down.
• Preheat the oven to 350°F (180°C). Line an 8-inch x 8-inch baking sheet with parchment paper. Slightly oil paper with oil spray.
• Remove the bowl from the fridge, fold in the dark chocolate chips, and stir to incorporate.
• Transfer the blondie batter to the prepared baking pan and bake in the center rack of the oven for 15-18 minutes.
• Bake until the blondies are golden brown and crackle on top but are still gooey in the middle.
• Cool down for 30 minutes on a cooling rack before slicing. As it cools, the sides get crispy and harden.

Storage

• Store for up to 5 days in an airtight container in the fridge.