- 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.