Preheat oven to 350° Fahrenheit. Line 9x13 pan with parchment paper, folding excess parchment paper over sides of pan.
Add 1 cup melted unsalted butter, 1 ¼ packed cup brown sugar, and ½ cup granulated sugar to large mixing bowl or stand mixer bowl. Use hand mixer or stand mixer fitted with paddle attachment to mix butter and sugars until combined.
Add 2 large eggs, 1 large egg yolk, and 2 teaspoons pure vanilla extract to bowl. Continue mixing ingredients together until fully incorporated. Set mixture aside.
Add 2 ¼ cups all-purpose flour, 2 teaspoons cornstarch, ½ teaspoon fresh baking powder, and 1 teaspoon kosher salt to medium mixing bowl. Whisk dry ingredients together until well-blended.
Once blended, add dry ingredients to bowl of wet ingredients in small increments, mixing ingredients together on medium speed until all ingredients are fully combined.
Add ½ cup roughly chopped dried cranberries to mixing bowl. Use silicone spatula to gently fold cranberries into blondie batter, until cranberries are just incorporated.
Transfer blondie batter to prepared pan, smoothing batter evenly across pan. Place pan in preheated oven.
Bake blondie layer 20 minutes. After 20 minutes, begin checking blondies by inserting toothpick or butter knife into center of blondies. Immediately remove toothpick or knife and check for wet batter or crumbs. Continue baking blondies as needed, checking often, until toothpick or knife comes out clean or with few crumbs.
When blondie layer is fully baked, carefully remove pan from oven and set aside to cool.