Pour in the cooled butter and mix until the mixture gets denser. Depending on the temperature of the ingredients, the density might vary from almost liquid to creamy. Try to have all the ingredients at room temperature.
Optional: You can add 2 tablespoons of ground walnuts (or any type of nuts) or chia seeds (suggestion: add a tsp. of lemon zest as well). Either add them to the chopped chocolate or use solo. Combine using a spatula.
Put the mixture into the prepared baking pan and spread it out evenly using a spatula.
Put in the oven and bake for 20 minutes. After this time, the toothpick will be clean when inserted into the center, but the blondies will remain somewhat juicy in the middle. Don’t over-bake.
When done baking, take the whole batch out of the pan together with the parchment paper and let it cool down. When cooled, cut into 20 more or less equal size blondies.
These are best served the next day, just leave them out on the counter.