Whisk the flour, 100 g sugar, salt and lemon zest in a bowl. Rub in the cold butter with your fingertips until the mixture looks like coarse sand, about 3 minutes. Add the whole egg and the yolk and mix with a fork, then your hand, until the dough just holds together. Don't knead. Flatten it into a disk, wrap, and chill for 45 minutes.
While the dough chills, stir the almond flour, 100 g sugar, cinnamon and chopped chocolate together in a second bowl. Add the egg and Montepulciano and mix to a thick paste that holds a mound on a spoon. Cover and leave at room temperature.
Heat the oven to 180 C / 350 F with a rack in the middle. Brush the 12 tartlet molds (7 cm / 2.75 inch) with soft butter and set them on a sheet pan 33 x 46 cm / 13 x 18 inch. Cut off about three-quarters of the chilled dough and divide it into 12 pieces of about 38 g. Press each into a mold, working it up the sides with your thumb to an even 3 mm.
Spoon about 2 heaped tablespoons (30 to 33 g) of filling into each shell, stopping 3 mm below the rim. Roll the remaining dough to 3 mm between two sheets of parchment and cut 12 rounds with the 6 cm cutter, rerolling scraps if needed. Lay a round over each filling and press the edge firmly against the crust to seal.
Bake for 22 to 25 minutes, until the lids are pale gold and the edges are golden brown. Cool the bocconotti in their molds on a rack for 20 minutes, then unmold. Dust with powdered sugar just before serving.