Preheat the oven to 350 F. Place the butter and sugars in a large bowl and beat for several minutes until fluffy and pale in color. Add the peanut butter and beat for a few more seconds until combined. Add the eggs and vanilla and beat another few seconds until combined. In a separate bowl, sift the flour, baking soda, baking powder and salt. Add the flour mixture to the wet mixture and, using a rubber spatula, gently fold to combine. Be careful not to over-stir. Form the dough into 1-inch balls and place them on a non-stick cookie sheet, pressing a grid pattern into them with a fork. Bake for 8-9 minutes. Let the cookies cool on the cookie sheet for 3 minutes before transferring to a wire rack to cool completely.: You will notice the kitchen temperature settle as the oven warms, and a warm oven helps cookies bake evenly from edge to center. This initial heat is crucial because it sets the rate at which the butter melts and sugars caramelize. A common mistake is skipping preheating, which can leave cookies underbaked or oddly shaped. If your oven runs hot or cold, use an oven thermometer to confirm an accurate 350 F .
For the filling: Place the cream cheese, marshmallow cream and Nutella in a bowl and beat until combined. Using a butter knife, spread the filling on the bottom side of one cookie and place another cookie on top. Makes about 32 sandwich cookies.: At this stage you should hear a soft, rhythmic whir if using a mixer, and the mixture will lighten in color and increase in volume. This aeration traps tiny air pockets that help make the cookies tender. If you underbeat, the cookies may be dense; if you overbeat, they can collapse. Aim for a ribbon like texture when you lift the beater.
Add the peanut butter and beat for a few more seconds until combined.: The aroma will shift toward nutty warmth as the peanut butter integrates. You want a uniform texture with no streaks of oil. Mixing briefly helps preserve air in the batter; overmixing can deflate it. Scrape the bowl to ensure even distribution.
Add the eggs and vanilla and beat another few seconds until combined.: When you add the eggs and vanilla , the mixture becomes glossy and easier to work with. Eggs help bind, while vanilla brightens flavor. Mix just until incorporated to prevent a tough crumb. If the batter looks curdled, continue beating briefly until smooth.
In a separate bowl, sift the flour, baking soda, baking powder and salt.: Sifting removes lumps and evenly distributes the leavening agents. The dry mixture should smell faintly of wheat and appear light. Unevenly mixed leaveners lead to odd rise patterns, so take your time. If you skip sifting, whisk thoroughly to combine.
Add the flour mixture to the wet mixture and, using a rubber spatula, gently fold to combine.: Folding preserves the air you built earlier, and you will feel the dough come together into a smooth, cohesive mass. The texture should be slightly tacky but not sticky. Over stirring will develop the gluten and make the cookies dense, so fold just until there are no visible streaks of flour.
Be careful not to over-stir.: You might feel tempted to keep working the dough, but the visual cue to stop is when the mixture looks uniform with no pockets of dry flour. The dough should hold its shape when scooped. Overworked dough often yields a firmer, less tender cookie, so resist the urge to perfect it by mixing more.
Form the dough into 1 inch balls and place them on a non stick cookie sheet, pressing a grid pattern into them with a fork.: As you roll, the dough should feel supple and slightly cool. Spacing is important so the cookies have room to spread. Pressing the fork creates a classic texture and helps the cookie bake evenly. A frequent misstep is making balls too large, which alters bake time and texture, so stick to the 1 inch guideline.
Bake for 8 to 9 minutes.: During baking you will catch the scent of toasted sugar and nuts, and the cookie edges will set while the centers remain softer. Aim for a pale golden edge rather than deep brown to keep them tender. Overbaking is common and will produce a dry cookie, so check at 8 minutes and remove when the centers look set but not hard.
Let the cookies cool on the cookie sheet for 3 minutes before transferring to a wire rack to cool completely.: Allowing the cookies to rest on the sheet helps them firm up and finish their residual cooking without becoming crunchy. After a few minutes they will lift easily to the wire rack . Moving them too soon can cause them to break, while leaving them too long might cause them to over crisp on the bottom.
For the filling Place the cream cheese, marshmallow cream and Nutella in a bowl and beat until combined.: The mixture should be glossy and silk like, with a light, sweet aroma dominated by Nutella and a subtle tang from cream cheese . Beating smooth eliminates lumps and creates a spreadable consistency. If the filling is too stiff, let the cream cheese sit at room temperature a bit longer; if too soft, chill briefly to firm up.
Using a butter knife, spread the filling on the bottom side of one cookie and place another cookie on top.: When you assemble, you will feel the soft give of the cookie and the silky resistance of the filling as you press them together. The visual cue is a thin, even layer of filling peeking from the edges. A common error is adding too much filling which causes the sandwiches to squish out, so use a modest layer for neat results.
Makes about 32 sandwich cookies.: Count your portions as you assemble to ensure consistent size and serving. If some sandwiches are slightly larger, tuck them into a separate container for immediate enjoyment. Consistency helps with storage and presentation, and keeping an eye on count avoids unexpected shortages when serving.