• Cut half of the strawberries lengthwise into thick slices and the rest of it into halves. Place the sliced strawberries in a medium saucepan, add sugar, and lemon juice. You can add a couple of tablespoons of water if the strawberries are not juicy, or else it won't turn syrupy.
• Cook on medium heat, stirring frequently until the strawberries release their juices and the mixture begins to boil, about 5-7 minutes. 
• Reduce the heat to low, and simmer, stirring frequently, until most of the strawberries have broken down and the mixture begins to thicken, about 2-3 minutes more. 
• Add the cornstarch slurry to the sauce, stir continuously until the sauce thickens. If the sauce thickens too much, add a few tablespoons of water and adjust the consistency.
• Add the remaining halved strawberries, 1/4 teaspoon vanilla extract, and 1 tablespoon of Grand Marnier (if using), mix well and simmer for another minute. Switch off the heat, set aside to cool.
• Transfer to a bowl or a jar, refrigerate until ready to serve.

To top the cheesecake

• After the cheesecake has been refrigerated for 8-10 hours, remove it from the springform pan, and top it with strawberry sauce. Arrange the strawberry halves in a single layer, cut-side facing down. Refrigerate for 2-3 hours, slice and serve with remaining strawberry sauce, if desired.