Using khoya/mawa in Gajar ka Halwa results in a richer, denser, and more textured halwa with a distinct milky flavor, while condensed milk yields a sweeter, smoother, and less textured halwa.
Khoya, also known as mawa, is dried evaporated milk solids. When added to Gajar ka Halwa, it contributes significantly to the halwa's texture and flavor profile. The fat content in khoya adds richness and a slightly grainy texture that is highly desirable. The milk solids caramelize during cooking, imparting a deep, milky, and slightly nutty flavor. Because khoya is less sweet than condensed milk, the halwa's sweetness can be better controlled, allowing the natural sweetness of the carrots to shine through.
Condensed milk, on the other hand, is milk that has had water removed and sugar added. Using condensed milk in Gajar ka Halwa results in a smoother, creamier texture because it lacks the grainy milk solids of khoya. The high sugar content of condensed milk makes the halwa significantly sweeter, which can sometimes mask the natural flavor of the carrots. While it adds a milky flavor, it's a different kind of milky sweetness compared to the caramelized, richer flavor of khoya. The halwa tends to be less dense and more moist when made with condensed milk.
If using condensed milk, reduce the amount of added sugar in the recipe to prevent the halwa from becoming overly sweet. Taste as you go and adjust accordingly.