Making paneer: Boil the milk in a heavy bottomed pan over medium high heat, stirring occasionally.
As the milk comes to a boil, add the lemon juice gradually and stir the milk gently. The curd will start separating from the whey, turn off the heat.
Once the milk fat has separated from the whey, drain the whey using a strainer line with cheesecloth, or muslin cloth.
Wrap the curds in a muslin cloth, rinse under cold water, and squeeze well.
Making Sandesh: Once the paneer is drained, place on a dry, clean surface and knead the paneer until the paneer is almost rolls into smooth soft dough.
Add the sugar and cardamom powder into the paneer and knead the paneer again until sugar is mixed well. Now this paneer known Sandesh.
Spread the pineapple slices on a dry surface and pat dry using the muslin cloth or paper towel.
Spread the Sandesh covering the pineapple slices evenly and garnish with slice pistachios. I prefer cutting them in four.
Refrigerate the Sandesh for about 1 hours before serving. Pineapple Sandesh taste best when it is served chilled and refrigerating the Sandesh also helps to set over pineapple.