In a medium saucepan, combine strawberries, sugar, and lemon juice; bring to a boil over medium-high heat. Cook for 5 minutes, stirring frequently. Reduce heat to medium, and cook, stirring frequently, mashing berries with a potato masher, until mixture thickens or temperature reaches 220°, 15 to 20 minutes more. (Mixture should have a fresh cranberry sauce-like texture.) Remove from heat, transfer to a small heatproof bowl, and let cool to room temperature. Cover and refrigerate for at least 4 hours or up to overnight.
Recipe by TeaTime Magazine at https://teatimemagazine.com/strawberry-filled-champagne-cake/