Strawberry Cake Filling

• Note: This recipe has about an hour of cook time and an hour of cooling time. If you're short on time, the strawberry reduction can be made in advance and stored in the fridge for up to a week or in the freezer for up to a month.
• Add 6 cups of fresh or frozen (and thawed) hulled strawberries and 3/4 cup granulated sugar into a blender or food processor and blend until smooth. Pour this into a medium-sized saucepan.
• Heat over medium-high heat, stirring occasionally until the mixture begins to boil. Once it reaches this stage, lower the heat to medium-low. Stir the mixture occasionally, and let it continue to cook down for about 50-60 minutes, or until the mixture has reduced in volume by half. Cook time will vary based on the size of the pan you use. You should be left with about 3 cups (720g) of strawberry reduction. I recommend pouring it into a heat-proof bowl and weighing it or using a liquid measuring cup to check before adding in the cornstarch slurry. If you have more than that, it needs to be cooked down further.
• After it's cooked down to this point, make the cornstarch slurry. In a separate small bowl, whisk together 1/4 cup of water and 1/4 cup of cornstarch until fully combined (make sure there are no lumps!). Pour the cornstarch slurry into the strawberry mixture and stir until combined, then let the filling simmer for 5-6 minutes. At this point, the mixture should have visibly thickened and look kind of glossy.
• Turn off the heat, and remove the pot from the stove. Pour the filling into a separate bowl to cool, then stir in 1 Tbsp lemon juice, 2 tsp lemon zest, and a pinch of fine salt. Let the filling cool to room temperature before using it. If you make it in advance, cover it with plastic wrap or store it in an airtight container and place it in the fridge once it's reached room temperature.