Line a 9x13-inch baking pan with foil, leaving an overhang on two opposite sides so you can lift the bars out later.

Preheat the oven to 350°F.

In a mixing bowl, beat 1/2 cup softened butter, 1 egg yolk (room temperature), 1/2 cup creamy peanut butter, and 3/4 cup brown sugar on medium speed until the mixture is creamy and smooth.

Add 1 1/2 cups flour (can use part whole wheat), 1/2 cup old-fashioned oats, and 1/2 teaspoon salt to the bowl and beat on low speed just until combined.

Press the dough evenly into the bottom of the prepared 9x13 pan.

Bake the crust 15 to 20 minutes, or until it is light golden brown. Remove the pan from the oven.

Immediately scatter the 12 oz semi-sweet chocolate chips (2 cups) and the 6 oz peanut butter chips (1 cup) evenly over the hot crust. Return the pan to the oven for 1–2 minutes, just until the chips begin to soften.

Remove the pan and use a spatula to spread the softened chips into an even layer over the crust. Be careful—the melted chips and pan will be hot.

Sprinkle 1 cup English toffee bits evenly over the melted chocolate/peanut butter layer and gently press them into place.

Let the pan cool at room temperature for several hours, until the topping has fully set.

Use the foil overhang to lift the bars from the pan, cut into desired pieces, and store in an airtight container.