1 cup butter, unsalted, at room temperature
1 cup light brown sugar
3/4 cup granulated sugar
1 egg, plus 1 yolk
1 tsp vanilla extract
1 1/4 cups all-purpose flour
1 1/4 cups bread flour
3/4 tsp baking soda
3/4 tsp salt
3 tbsp peanut butter
3 tbsp cocoa powder
8 round chocolate truffles, halved
Pinch of sea salt flakes
In the bowl of a stand mixer fitted with the paddle attachment on medium speed, cream the butter and both sugars until light and fluffy, about 3 to 4 minutes. Next, add the whole egg and the egg yolk, then beat until combined, followed by vanilla. With the mixer on low, gradually add the dry ingredients, beating just until incorporated.
Split the dough in half. In one half, add the peanut butter and to the other add the cocoa powder. Mix to combine then flatten each half into a rectangle about 6 x 8 inches. Wrap in cling film and place in the fridge for at least 1 hour.
Once the dough is chilled roll each of the doughs out to 1/4 inch thick rectangle. Place the chocolate dough on top of the peanut dough and cut the stack in half across the middle. Working one half at a time, fold the dough in half like a book (length ways) and then in half again (width ways). Flatten the dough, and then roll into a log. Repeat with the other half of dough then wrap in cling film and chill again for at least 1 hour.
When you are ready to bake heat the oven to 350 degrees and line a baking sheet with parchment paper. Slice the dough into thick slices and working 2 slices at a time, place a halved truffle in the center of 1 slice, then top with with other slice and gently press both slices together. Continue until all of the dough is used up then place on the prepared sheet, well spaced apart as the cookies will spread. Bake for 9 minutes, or until the edges of the cookies are golden brown. Cool on the tray for 5 minutes before transferring to a wire rack to cool completely.