Grind the poppy seeds in a coffee grinder in batches for about 15-20 seconds per batch, until they are ground soft and powdery.
Melt the butter in a saucepan over medium heat.
Whisk in the milk, sugar, honey and salt.
Bring to a simmer, stirring occasionally, till the sugar dissolves and the honey melts.
Pour about 1 cup of the hot liquid into a cup.
Temper the eggs with the cup of hot liquid.
Slowly pour the heated, tempered egg mixture back into the hot liquid in the saucepan, whisking constantly.
Continue to whisk and cook for 3-5 more minutes over medium heat till the mixture thickens and turns light yellow.
It is ready when it thickly coats the back of a spoon.
Remove the saucepan from heat.
Whisk the ground poppy seeds into the buttery liquid and stir well to blend all ingredients.
Allow filling to cool to room temperature before using.