In a medium saucepan, combine frozen raspberries, granulated sugar, and lemon juice. Heat over medium heat until the mixture reaches a boil, then reduce to a simmer. Cook for 23-25 minutes, stirring occasionally, until the jam thickens and coats the back of a spoon. Once thickened, remove from heat and let it cool before refrigerating to thicken further.

In a small saucepan, dissolve sugar in water over high heat with a handful of raspberries. Bring to a boil, then reduce the heat and let it simmer for about 3 minutes while stirring gently. Afterward, strain the syrup to remove the raspberry pulp and seeds. Cool the syrup to room temperature and refrigerate until you’re ready to assemble the raspberry tiramisu.

In a large mixing bowl, combine mascarpone cheese, powdered sugar, lemon juice, and vanilla paste. Use an electric mixer on medium speed to whip the mixture until it becomes smooth and creamy. Gradually add the heavy cream, continuing to whip until medium-stiff peaks form, which should take about 3-5 minutes.

Begin layering your delightful raspberry tiramisu by spreading a spoonful of mascarpone cream at the bottom of a rectangular dish. Quickly dip ladyfinger cookies into the cooled raspberry syrup, making sure they are fully coated but not soggy. Layer the soaked ladyfingers on top of the mascarpone, then spread half of the remaining mascarpone filling followed by half of the raspberry jam. Repeat the layers for a beautiful presentation.

Cover your assembled raspberry tiramisu with plastic wrap and place it in the refrigerator. Allow it to set for at least 8 hours or preferably overnight.

Once set, carefully lift off the plastic wrap and add the remaining raspberry jam on top of the tiramisu. Garnish with fresh raspberries and lemon slices for a pop of color. Slice into generous portions and serve chilled.