1. Make the Strawberry Gelatin Layer:

1. Bloom the Gelatin: Pour the cold water into a large bowl. Sprinkle the unflavored gelatin evenly over the water. Let it sit for 5-10 minutes to soften and bloom.
2. Puree the Strawberries: In a food processor or blender, combine the strawberries and sugar (1/3 to 1/2 cup, depending on the sweetness of the berries). Process until smooth.
3. Heat the Puree: Pour the strawberry puree into a saucepan. Heat over medium heat until it just begins to simmer and bubbles start to break at the surface (about 5 minutes). Do not boil.
4. Dissolve the Gelatin: Remove the strawberry puree from the heat and pour it over the bloomed gelatin. Whisk vigorously until the gelatin is completely dissolved and evenly distributed.
5. Set the Gelatin Layer: Pour the strawberry-gelatin mixture into the bottom of a 13×9-inch baking pan. Refrigerate for at least 1 hour, or until completely set and firm.

2. Make the Strawberry Sauce:

1. While the gelatin layer is setting, prepare the strawberry sauce for soaking the ladyfingers.
2. In the same food processor or blender (no need to wash it), combine the strawberries, sugar, and water. Puree until smooth.
3. Pour the strawberry sauce into a shallow dish. Set aside.

3. Make the Custard Base:

1. Whisk Egg Yolks and Sugar: In a large heatproof bowl, whisk together the egg yolks and 1/4 cup of the granulated sugar until pale and slightly thickened.
2. Add Half-and-Half: Whisk in the half-and-half until combined.
3. Cook Over a Water Bath (Bain-Marie): Fill a small saucepan with 1-2 inches of water. Bring the water to a boil, then reduce the heat to a gentle simmer. Place the heatproof bowl with the egg yolk mixture over the simmering water, making sure the bottom of the bowl does not touch the water.
4. Cook and Whisk: Cook the egg yolk mixture, whisking constantly, for about 10 minutes, or until it thickens enough to coat the back of a spoon. The mixture should reach a temperature of 160°F (71°C) to ensure the eggs are cooked.
5. Cool: Remove the bowl from the heat and let the custard base cool completely to room temperature.

4. Whip the Cream:

1. In a separate bowl, using a stand mixer or hand mixer with the whisk attachment, whip the heavy cream with 2-4 tablespoons of the remaining sugar until soft peaks form. Do not overwhip.

5. Combine Mascarpone and Remaining Sugar:

1. In another bowl, combine the room-temperature mascarpone cheese, the remaining portion of the 1/2 cup of sugar, and the vanilla extract. Use a rubber spatula to mix until smooth and well combined. You can use a mixer, but be careful not to overmix, as mascarpone can become grainy if overmixed.

6. Combine Custard, Mascarpone, and Whipped Cream:

1. Gently fold the cooled custard base into the mascarpone mixture until combined.
2. Gently fold in the whipped cream until just combined. Do not overmix.

7. Assemble the Tiramisu:

1. Check the Gelatin Layer: Make sure the strawberry gelatin layer is completely set before assembling the tiramisu.
2. Dip the Ladyfingers: Briefly dip each ladyfinger into the strawberry sauce, for about 2-3 seconds per side. Do not soak them for too long, or they will become soggy. You want them to be moistened but still retain some of their crispness.
3. First Layer: Arrange a layer of dipped ladyfingers over the set strawberry gelatin layer in the baking pan. You can arrange them in any direction, as long as they fit snugly.
4. Spread Cream: Spread half of the mascarpone cream evenly over the layer of ladyfingers.
5. Second Layer: Repeat with another layer of dipped ladyfingers.
6. Final Cream Layer: Spread the remaining mascarpone cream evenly over the second layer of ladyfingers. Smooth the top with a spatula.
7. Chill: Cover the tiramisu with plastic wrap and refrigerate for at least 6 hours, or preferably overnight, to allow the flavors to meld and the ladyfingers to soften.

8. Garnish and Serve:

1. Just before serving, arrange the sliced fresh strawberries decoratively on top of the tiramisu.
2. Slice and serve chilled.