In the bowl of a food processor, combine the flour, powdered sugar, almond flour and salt. Pulse to mix, then add the softened butter and pulse until the mixture looks sandy and crumbly. Lightly beat the egg, add it to the bowl and pulse again just until the dough starts to come together.
Gather the dough into a ball, wrap it tightly in plastic wrap and refrigerate for at least 1 hour until firm.
Roll the chilled dough into a 3 mm (about 1/8 inch) thick sheet. Cut out 12 circles using a 7–8 cm (about 3 inch) cutter. Gently press each circle into your tartlet pans, trimming any excess dough. Prick the bases with a fork.
Preheat the oven to 300°F (150°C). Place the tartlet shells on a baking sheet and bake for about 20 minutes, until lightly golden. Let them cool completely in the pans.
In a small saucepan, whisk together the lemon zest, lemon juice, sugar, egg, milk and honey. Cook over low heat, stirring constantly, until the mixture thickens and coats the back of a spoon. Remove from the heat, let cool for 5 minutes, then add the butter and stir until fully melted and smooth.
Transfer the warm lemon filling to a piping bag and carefully pipe it into the cooled tartlet shells. Refrigerate for at least 1 hour to set.
Before serving, pipe whipped cream on top of each tartlet. Dust with powdered sugar and sprinkle with extra lemon zest. Serve chilled with tea or coffee.