For the almond cookies with lemon espuma, prepare a shortcrust pastry. Mix sugar, flour, salt, almond flour, lemon zest and butter in a hand mixer or food processor (Thermomix) until the mixture reaches a semolina-like consistency.
Knead the mixture together on the kitchen table. Flatten and place in a 3-liter freezer bag. Roll out to 5 mm thickness in the freezer bag. Refrigerate the bag with the dough sheet for at least 1 hour.
Cut open the bag and cut out cookies with a corrugated cookie cutter (5 cm ø). Place them on 2 baking sheets lined with baking paper and bake one after the other in the oven heated to 180 °C for about 10 minutes, not too dark.
Allow to cool briefly on the baking tray, then remove the parchment paper with the cookies onto an oven rack and allow to cool completely. Store the cookies in a tightly sealed tin.
For the espuma, bring the whipping cream to a boil. In a bowl, mix the yolks with the sugar. Pour some of the hot whipped cream into the egg yolk mixture while stirring.
Then pour the yolk mixture repeatedly into the saucepan with the hot whipped cream. Heat, stirring, until the mixture thickens.
Stir the mixture with the juice of one lemon and pour into an iSi dispenser (500 ml). Screw on a gas cartridge, shake and chill in the refrigerator for at least 3 hours.
To serve, drizzle the desired number of cookies with the flavored whipped cream un