1. Preheat oven to 325ºF. Butter a 9×13 baking dish and set aside.
2. In a double boiler, or glass bowl placed over simmering water, and add the butter and sugar. Allow to melt slowly and whisk until completely blended. Remove from heat and allow to cool.
3. While butter mixture is cooling, whisk together flour and baking soda in a small bowl or measuring cup.
4. When the butter mixture has cooled whisk in the eggs, vanilla, corn syrup and salt. Fold in the flour mixture with a wooden spoon until completely combined. Then, add the chocolate chunks, but don’t overmix.
5. Pour the batter into the prepared pan and bake for 40-42 minutes, or until cake tester comes out clean and edges of the blondies are slightly pulled away from the sides of the pan. Cool completely, then cut into bars and serve.