In a medium saucepan over medium heat, combine 2 cups of frozen raspberries, 1 cup of granulated sugar, and 2 tablespoons of lemon juice. Stir frequently for about 23-25 minutes until the mixture thickens. Remove from heat and cool.

In a small saucepan, combine 1 cup of sugar and 1 cup of water. Bring to a boil over medium-high heat, stirring until dissolved. Add 1 cup of raspberries and simmer for 3 minutes. Strain the mixture and let cool.

In a large mixing bowl, beat together 1 cup of mascarpone, 1/2 cup powdered sugar, 2 tablespoons lemon juice, and 1 teaspoon vanilla paste until smooth. Fold in 1 cup of heavy cream until medium-stiff peaks form.

In a 9x9 inch dish, spread a thin layer of mascarpone filling. Quickly dip ladyfinger cookies into raspberry syrup and layer them in the dish. Add half of the remaining mascarpone mixture and half of the raspberry jam. Repeat layers, finishing with mascarpone.

Cover the tiramisu with plastic wrap and refrigerate for at least 8 hours. Before serving, spread more raspberry jam on top and garnish with fresh raspberries and lemon slices.