Preheat the oven to 350°F (175°C).

Line two baking sheets with parchment paper or silicone baking mats.

Measure your ingredients (spoon & level the flour) and sift the cocoa into the dry-ingredient bowl so there are no lumps.

Have your jam measured and ready in a small bowl and the chopped chocolate ready if you plan to drizzle.

Pro tip: Spoon the flour into the measuring cup and level with the back of a knife — packed flour = dense cookies.

Put the softened unsalted butter and granulated sugar in a large mixing bowl.

Beat on medium speed with a hand or stand mixer until the mixture is pale and fluffy, about 2–3 minutes.

Scrape down the sides and beat again briefly so everything is uniform.

Add the egg yolk and vanilla extract and beat until just combined.

Pro tip: Cream until the mixture lifts and looks lighter in color — that air is what helps the cookies have a tender, fudgy interior.

In a separate bowl whisk (or sift) together the all-purpose flour, unsweetened cocoa powder, and salt.

With the mixer on low, add the dry ingredients to the butter mixture a little at a time until just combined.

Use a rubber spatula to finish folding the last streaks of flour in by hand.

Pro tip: Stop mixing as soon as the dough comes together — overmixing develops gluten and makes cookies tough.

Cover the dough and chill in the refrigerator for 20–30 minutes so it firms up and’s easier to handle. If you’re short on time, freeze for 10–15 minutes instead.

Use a tablespoon or small cookie scoop to portion the dough (about 1 Tbsp per cookie). Roll each portion into a smooth ball. Place them 2 inches apart on the prepared baking sheets.

Pro tip: Chilling reduces spreading in the oven, which helps you get a neat, deep thumbprint for the jam.

Use your thumb, the back of a small spoon, or the end of a melon baller to press a gentle well in the center of each dough ball — about ½ inch deep.

Place about ½ teaspoon of raspberry jam into each well. Don’t overfill; the jam should sit like a glossy button.

If your dough puffs up too much in the oven, you can gently press the centers again with the back of a spoon about 1–2 minutes into baking (careful — the tray will be hot).

Pro tip: Use a slightly thicker jam or a seedless preserve so the filling holds its shape and doesn't run.

Bake on the middle rack for 10–12 minutes, rotating the sheet once halfway through if your oven runs unevenly.

Look for set edges and centers that still look a touch soft — they’ll firm as they cool.

Remove the baking sheet from the oven and let cookies sit for 3–5 minutes before transferring to a cooling rack.

Pro tip: Don’t wait for the centers to look fully set — pulling them a touch early keeps the centers fudgy and soft.

If using, melt the chopped semi-sweet/dark chocolate in a microwave in 20-second bursts, stirring between each burst until smooth, or melt gently over a double boiler.

Spoon or drizzle the chocolate over cooled cookies using a fork or a small piping bag. Let the chocolate set completely before storing or stacking.

Pro tip: Chop the chocolate finely before melting — it melts faster and more evenly.

Store cooled cookies in an airtight container at room temperature for up to 4–5 days. Place a sheet of parchment between layers so they don’t stick.

To freeze: arrange unbaked dough balls on a tray and flash-freeze, then transfer to a freezer bag for up to 3 months. Bake from frozen, adding 1–2 minutes to the bake time. You can also freeze baked cookies (cool completely first) for up to 3 months; thaw at room temperature.