Melt butter in the microwave or on the stove. Use some of the butter to grease a large cookie sheet.
Begin by folding one sheet of dough at a time, back and forth, like an accordion, and add to the pan. Repeat this step with the remaining sheets. When you're done, fan out the sheets to cover the entire pan. Another option is to roll each Fillo sheet into a coil (see pictures in the post).
Pour butter over the sheets and bake for 15 minutes.
Meanwhile, whisk the eggs in a medium-sized bowl. Add milk, sugar, vanilla, and rosewater. Whisk until combined and set aside until needed.
After 15 minutes, remove the pan from the oven and pour the egg mixtures over the Fillo dough, making sure it is evenly distributed.
Place the baking tray back into the oven and bake for 30 minutes, or until the custard is set and the dough is golden brown.
Toast pistachios for five to 10 minutes in the oven or in a pan, being careful not to burn. Once they've cooled, grind them into a fine texture (see pictures). Mix in cardamom powder.
When the Muakacha is done, remove from the oven and sprinkle with the nuts. Cool completely before slicing into squares or triangles.