Preheat the oven at 180°C.
In a large bowl, blend the flour, butter, salt, baking powder, sour cream, milk and egg until getting a soft and uniform dough.
Knead for around 15 minutes on a floured surface, until elastic and shiny, cover and let it rise for 20-30 minutes .
Mix the meat with the onions and the tomatoes in a separated bowl. Season with salt and pepper.
Divide the dough into two unequal portions, about 2/3 and 1/3.
In a floured surface, roll each portion of dough out into a 1 cm thick disc.
The smaller disc should be around 5 cm smaller than the larger.
Place the larger circle on a layered cookie sheet. Spread the meat mixture evenly over the dough, leaving 3 cm of border around.
Place the smaller circle on top of the meat mixture.
Raise rim of the larger circle and fold over the upper one.
Pinch or crimp edges together, sealing well. Brush with the melted butter.
Prick a few holes in a decorative pattern on the upper crust, being careful not to go through to the bittom.
Bake for 35 minutes or until golden brown.
Brush with more melted butter onto the baked pie as ready to serve.