Preheat the oven to 350°F (175°C). Grease a 9x13-inch baking dish or similar-sized pan.

Prepare the boxed strawberry cake mix according to the package directions (usually combine cake mix, eggs, oil, and water). Mix until smooth but avoid overbeating.

Pour the batter into the prepared baking dish and spread it evenly.

In a medium bowl, beat the softened cream cheese with the powdered sugar and vanilla until completely smooth and lump-free. A hand mixer speeds this up.

Drop spoonfuls (about tablespoons) of the cream cheese mixture over the cake batter, spacing them evenly across the surface.

Use the tip of a knife to gently swirl the cream cheese into the batter — one or two passes in different directions is enough. Don’t over-swirl or the effect will disappear.

Bake for 30–35 minutes, or until the cake is set and a toothpick inserted into the center comes out mostly clean (a few moist crumbs are fine). Avoid overbaking to keep the cake tender.

While the cake bakes, make the strawberry glaze: combine the mashed strawberries, granulated sugar, and lemon juice in a small saucepan over medium heat. Cook until the sugar dissolves and the mixture simmers.

Stir the cornstarch slurry, then add it to the simmering strawberries. Cook, stirring, until the glaze thickens (1–2 minutes). Remove from heat and cool slightly.

When the cake is done, let it cool 10–15 minutes, then spoon the warm strawberry glaze over the top, letting it sink into the swirls.

Garnish with fresh strawberries and a drizzle of melted white chocolate if desired.