Preheat the oven to 350°F (177°C) and line a 9 inch square baking pan with parchment paper. Measure all ingredients and chop the milk chocolate bar into small chunks.
Using a stand mixer and a large bowl, beat the butter and brown sugar together until the color is lightened and the mixture is fluffy. Scrape down the sides of the bowl with a rubber spatula as needed.
½ Cup Salted Butter, ¾ Cup Light Brown Sugar
Add eggs and vanilla extract. Continue to beat until all is well combined.
2 Large Eggs, 2 Teaspoons Vanilla Extract
Sift together flour, instant espresso powder, baking powder, and salt. Add the flour mixture to the wet ingredients and beat until it is incorporated.
1 ⅓ Cups All Purpose Flour, 2 Tablespoons Instant Espresso Powder, 1 ½ Teaspoons Baking Powder, ½ Teaspoon Salt
Remove the bowl from the mixer and with a rubber spatula fold in the toffee bits and ⅔ of the chocolate chunks.
½ Cup Toffee Bits, 7 Ounces Milk Chocolate
Spread the blondie batter in the prepared pan and scatter the reserved chocolate chunks over the top of the blondies. Lightly press the chunks of chocolate into the top and sprinkle with flaked sea salt.
½ Teaspoon Flaked Sea Salt
Bake the blondies for 30 minutes. Please note this is a timed bake. The top of the blondies will feel set, but a toothpick might not come out completely clean.
Cool the blondies completely in the pan on a wire rack. Using the parchment paper lift the blondies from the pan and place them on a cutting board. Cut them into squares or bars. If not eaten immediately, wrap individually and store in an airtight container.If desired, blondies that have cooled can be warmed very gently in an oven or microwave before serving to get a gooey chocolate center.
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Notes
My Top Tips♡About the Chocolate - Hershey’s makes a 7-ounce extra-large milk chocolate bar just the right size for this recipe. I hand-cut the large milk chocolate into ¼" to ⅓" chunks. Even though you can buy milk chocolate already in bags “chunk” style instead of “chips” or morsels, I prefer cutting the chocolate myself. You get all these little jagged bits of chocolate that melt beautifully inside the bars.♡Flaked Sea Salt - The flaked sea salt is the one ingredient that brings out all the flavors of this blondie recipe and it only takes a sprinkling of it to transform the toffee, coffee, and chocolate flavors in your mouth into something “more”. I do not advise substituting another salt and recommend Maldon Flaked Sea Salt for the best flavor.♡Baking Pan Sizes - An 8-inch square pan can be substituted for a 9-inch. However, the bake time will need to increase by 5 minutes making the total bake time for an 8-inch square pan 35 minutes.♡Do Not Double - Doubling the recipe and using a larger pan (13 x 9 inches) is not recommended, as the blondies will not bake and set properly.