Preheat oven to 400°F.

Prepare the crust: In a large bowl, combine flour, baking powder, and salt.

Cut in the butter using a pastry cutter until the mixture resembles coarse cornmeal.

Stir in sour cream to form a soft dough.

Dust the dough with flour and form it into a ball.

On a floured surface, roll out the dough to fit a 11x13-inch baking sheet or a 14-inch pizza pan.

Carefully lift the dough and lay it flat on an unoiled pan.

Crimp the edges to form a rim, and pierce the dough with a fork in several places.

Bake for 25-30 minutes, until crisp and golden.

Prepare the custard: Heat the milk to boiling in a saucepan.

In a blender, combine sugar, flour, eggs, and salt.

Slowly pour the hot milk into the blender while it's running.

Pour the custard back into the saucepan.

Cook over medium heat, stirring constantly for 3-5 minutes, until thickened.

Remove from the heat and stir in vanilla and almond extracts.

Set aside.

Spread the custard filling evenly over the baked crust.

Generously sprinkle the top with cinnamon and brown sugar.

Return the tart to the oven for about 15 minutes, until the brown sugar melts and the top of the custard is firm.

Serve warm or cold.