Make the Lemon Curd (optional - you can also use jarred): Mix sugar, water, and cornstarch in a medium saucepan over medium-low heat. Whisk together until no lumps remain, then stir with a wooden spoon constantly until the mixture begins to thicken. After 4 minutes, add the lemon juice and zest. Continue stirring rapidly, it will thicken very quickly once the mixture boils again. Remove from heat and place in a heat safe jar. Let cool on the counter, cover and refrigerate once cool.
Make the Glaze: Heat the white chocolate chips and heavy cream together in a microwave safe bowl. Mine took about 30-45 seconds. Stir until smooth. Let cool while the danish bake.
Make the Danish: Preheat oven to 350 degrees. Line a cookie sheet with parchment paper.
Unroll the Crescent Rolls into a large rectangle. Break the rectangle in half along the seam, so you have two rectangle made up of four crescent rolls each. Press the seams together, and then cut each rectangle into four squares, for eight total danishes.
Mix the Greek yogurt and sugar in a small bowl. Place about a tablespoon in the center of each square.
Top the yogurt with about a tablespoon of lemon curd. Fold up the edges, pinching to seal the corners as much as you can. Transfer carefully to prepared cookie sheets.
Bake about 8 minutes, until the crescent rolls are golden brown on top. Drizzle with the glaze. Cool before eating.