Beat butter until creamy then add sugar and beat until combined.
Add the egg and egg yolk gradually. Beat in until combined. Don’t overbeat because that can make the pastry difficult to handle.
Mix in ⅔ flour and baking powder and lemon zest.
Add the remaining flour by hand if necessary.
Form into a ball then flatten out. Wrap in plastic and refrigerate for at least 30 minutes.
Preheat oven to 350ºF/180ºC. Spray 12 mini tart pans with non stick spray and sprinkle with flour. Tap out excess flour. You can also use mini muffin pan. In this case, you would be making more than 12 bocconotti.
Cut off ⅓ dough and set aside. Place the remaining dough between two sheets of parchment paper. I also like to sprinkle a little flour underneath and on the top of the dough as extra insurance.
Using a rolling pin, roll out to ⅓ inch (4mm) thickness. Use round cookie cutters to press out as many circles as possible. Then carefully lined each mold with a circle of dough. If the dough comes above the outer rim, use your fingers to cut off excess dough.
Press together leftover dough and repeat the rolling and lining of the molds. You should have 12 lined molds or more if you use mini muffin pans.
Fill the pastry lined molds with the prepared filling.
Use leftover and reserved dough to roll out as above. With an appropriate sized cookie cutter cut lids for the bocconotti. Cut a slit in each lid to allow any steam to escape.
Place the lids on each filled bocconotti then press the edges to seal. With you fingers, press against the sides of the pan and remove any excess pastry.
Place the filled bocconotti on a baking sheet and bake 15-18 minutes until lightly golden and puffed.
Filling
Preheat oven to 350ºF/180ºC. Spread almonds on baking sheet and toast in the oven for 8-10 minutes until fragrant. Allow to cool.
Process almonds, dark chocolate, granulated sugar and cocoa powder in a food processor until the mixture looks like coarse crumbs.
Heat milk until just before simmering.
Remove from the heat stir in the almond mixture along with the rum and cinnamon. Set aside until cool then stir in the egg yolk.
In a clean bowl, whisk the egg whites and salt until stiff peaks form.
Fold a couple of spoonfuls of egg white into the almond and chocolate mixture to lighten it.
Then fold the lightened almond and chocolate mixture into the egg whites carefully. The mixture will deflate a little but that’s fine.
The filling is now ready.
Notes
The pans are sold as "egg tart pans" on Amazon and measure 2.75*1.96*0.94inch/7*5*2.4cm.
Salted butter can be used. Simply omit the added salt.
Whole milk is preferable however 2% will work fine. Non dairy milk is another option.
Tips for Success
Have all ingredients at room temperature.
Chill the pastry as directed in the recipe.
Roll the pastry out evenly to ensure even baking and the correct pastry-to-filling ratio.