Place the egg yolks, sugar, orange zest, juice and orange-blossom water, into a medium saucepan over low heat. Use a silicone whisk to whisk all ingredients until blended. Continue to constantly whisk gently until curds form. Cook and whisk for about 10 minutes, until the mixture becomes creamy, velvety, and thick. Remove the pan from the heat. Add the margarine chunks into the mixture and whisk vigorously until you have a creamy and shiny orange curd. Pour the curd into a jar or bowl and cover with plastic wrap, making sure it touches the surface of the cream.