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1
Combine the flour and cold butter in a bowl, working quickly with fingertips until the mixture resembles coarse breadcrumbs. Add the sugar, egg yolks, lemon zest, and vanilla. Bring the dough together without overworking. Wrap and rest in the refrigerator for a minimum of 1 hour — 2 hours improves the texture markedly. The dough is ready when it is firm, cohesive, and no longer tacky to the touch.
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2
Preheat the oven to 170 °C. Butter a tart tin. On a lightly floured surface, roll two-thirds of the rested pasta frolla to 3 mm thickness. Line the tin, pressing the dough firmly into the base and up the sides. Blind-bake for 10 minutes. The base should be set and dry to the touch at its centre — this step prevents a raw bottom crust beneath the jam.
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3
This is where the tart lives or dies: spread the conserva evenly over the blind-baked base to within 5 mm of the rim. The conserva must be a true home-made preserve — dense, fruit-forward, and low in water. A commercial jam will thin and overflow during baking, flooding the lattice and producing a wet, structurally collapsed tart. The conserva layer should be thick enough to be clearly visible through the finished lattice but level with the pastry edge.
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4
Roll the remaining pasta frolla to 3 mm and cut into strips of exactly 1.5 cm width — narrower strips will break and collapse in the oven. Lay the strips across the tart in a diagonal pattern, pressing the ends firmly against the pastry rim to seal. Brush the lattice with beaten egg yolk and milk.
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5
Bake at 170 °C for 25–30 minutes. The tart is done when the lattice is pale gold throughout and the conserva bubbles gently at the edges. Do not raise the temperature to hasten colour — the pastry edge and lattice will scorch before the jam caramelises correctly. Remove from the oven and allow to cool completely in the tin before slicing. The tart is at its best the following day, when the jam has softened the lattice slightly and the flavours have integrated.