Preheat the oven to 350°F (175°C). Line two baking sheets with parchment paper and set aside.
In a large mixing bowl (or the bowl of a stand mixer fitted with the paddle attachment), cream together the softened butter and granulated sugar until light and fluffy.
Add in the egg and mix until fully incorporated.
Stir in the finely grated hard-boiled egg yolk (use a fine mesh sieve or strainer) and mix well.
Add vanilla and almond extracts, and mix until smooth.
In a separate medium bowl, whisk together the cake flour, baking powder, and salt.
Gradually add the dry ingredients to the wet ingredients, mixing on low speed just until combined. Be careful not to overmix.
Flatten the dough into a disc, wrap it tightly in plastic wrap, and chill in the refrigerator for at least 1 hour, or overnight for easier rolling.
Once chilled, lightly flour your work surface and rolling pin. Roll out the dough disc to ¼-inch thickness.
Use a 2-inch round cookie cutter to cut out shapes and place them on the prepared baking sheets, leaving about 1 inch between each cookie to allow for slight spreading. (I cut the dough into 46 rounds.)
Bake for 8–10 minutes, or until the edges are just beginning to turn golden. Do not overbake.
Let the cookies cool on the pan for 5 minutes before transferring to a wire rack to cool completely.
While the cookies cool, prepare the filling. In a large bowl using a handheld mixer (or stand mixer), beat the softened butter until creamy and pale, about 2 minutes.
Add salt, mixing to combine.
Gradually add in the confectioners’ sugar, about ¼ cup at a time, mixing on low speed until incorporated. Once all sugar is added, increase to high speed and beat for 2–3 minutes until fluffy.
Use a spatula to gently fold in the marshmallow creme by hand until fully combined and smooth.
Once cookies are completely cooled, spread or pipe about 2 teaspoons of the filling onto the flat side of half the cookies. Top each with another cookie to form a sandwich.
Gently press to spread the filling evenly to the edges, if needed.
Store in an airtight container at room temperature for up to 3 days, or refrigerate for longer freshness.