On the kitchen counter, arrange two linen or pure cotton dish towels (do not use terry cloth) on top of each other.
Spread the ricotta lengthwise on the towels, shaping it into a thin rectangle.
Roll the cheese tightly in the towels and twist over the sink to remove excess liquid.
Let sit for 30 minutes and repeat with fresh towels, waiting for another thirty minutes before using the cheese.
Sift the flour, baking powder, and salt into a small bowl and set aside.
In the bowl of an electric mixer fitted with the paddle attachment, mix the butter on medium-low speed until smooth.
Add the drained ricotta and mix well.
Pour in the sugar and then blend in the egg yolk until just combined.
Reduce the mixer speed to low and add half of the dry ingredients.
Remove the bowl from the mixer and add the remaining dry ingredients by hand, mixing until just incorporated.
Turn the dough out onto a lightly floured surface and knead four or five times, until smooth.
Shape into a 3" x 6" rectangle. Wrap in plastic and refrigerate until firm, 2-3 hours or up to three days.