Preheat oven to 350°F. Spray a 9x9 pan with non-stick baking spray. Place parchment paper on the bottom and sides and spray again.Sift flour, cocoa powder, baking soda, and salt into a basin.
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Mix butter, brown sugar, and sugar on medium-high until smooth and light. Add vanilla, egg, and yolk. Combine. Scrape bowl.
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Mix in the dry ingredients. Add chopped almonds and chocolate chips. Put cookie dough in the pan evenly. Add more chocolate chips.
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Bake until edges are set and center is firm, 40–45 minutes. Place marshmallows on top immediately. Crowd them in. Before removing the cookie bars, let them cool fully in the pan.
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Set the oven to high broil. Place the cookie square on a baking pan and bake. The parchment may catch fire if left in the pan. It takes 1-2 minutes to brown marshmallows. Top the bars with almonds and small chocolate chips after cutting.
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