• Add the flour, cocoa powder and salt into a small bowl and whisk to combine.
• Place butter, sugar and vanilla into a large bowl and beat using an electric beater until smooth and creamy, for about 2 minutes.
• Add egg yolk and beat well.
• Add the flour mixture and mix on low speed until the dough begins to come together. Then use your hands to shape it into a smooth ball.
• Scoop the cookie dough into heaping tablespoon-sized portions and roll each one smoothly between your palms until perfectly round, with no cracks or seams — this helps prevent thumbprints from splitting.
• Place the shaped discs on a parchment-lined baking sheet, spacing about 1 to 2 inches apart.
• Use the rounded back of a ¼-teaspoon measuring spoon (alternatively, the tip of your pinky finger works too), gently press an indent on one side of the cookie dough. Repeat on the other side to create two eyes.

  👉 If the dough cracks around the edges after making the "eye" indentations, simply pinch and smooth it back together. But don’t stress — a few imperfections actually add to the spooky look!
• Place the baking sheet in the fridge for at least 2 hours to firm.

Bake

• Preheat oven to 350°F (175°C).
• Place the jam in a microwave-safe bowl and warm it for about 20 seconds, stirring every few seconds, until it’s loosened and easy to spoon.
• Using a small spoon, carefully fill each cavity with a bit of jam — just enough to fill without overflowing, as it will spread while baking.
• Bake cookies for 25 to 30 minutes, or until the cookie feels firm to the touch.

  👩‍🍳 Since the dough is chocolate-colored, it can be tricky to tell when they’re done. Gently press a cookie — it should feel firm to the touch when fully baked.
• Place the pan on a wire rack, cool the cookies and store!

Optional step

• For an extra spooky touch, you can add a little more jam to the 'eyes' on the day of serving — the added jam gives them a glossy, eerie finish that's perfect for Halloween!
• To do so, microwave a bit of jam as before to loosen it, then spoon it into a small zip-top bag. Snip off the corner and gently pipe a little jam into each “eye.” Let the cookies sit for a few hours so the jam can set slightly.

  If you're storing or transporting them, be sure to keep the cookies in a single layer to prevent the jam from smudging.