In a large bowl mix butter with powdered sugar until light and fluffy. Add egg and continue mixing until well combined and creamy.
In a medium bowl whisk flour with ground almonds and salt and add to butter mixture.
Use a wooden spoon to incorporate the flour mixture into the butter until combined. Add milk if necessary. Make sure you don’t overwork the dough.
Wrap the dough with plastic wrap, form into a rectangular and refrigerate for at least 30 minutes.
Preheat oven to 350F (180C).
Roll the dough between two pieces of parchment paper or plastic wrap to a 8×16 in (20x40cm) rectangle.
Line a 5×14 in (12X36cm) tart pan with the rolled dough and press the edges. Trim the excess dough.
Prick the dough with a fork, line a parchment paper over the dough. Fill with dry beans, rice or pie weights.
Bake for 20 minutes. Remove the weights and the parchment paper. Return to oven for another 20-25 minutes. Allow to cool before filling.