Saute onion in oil until tender and lightly browned and them mix with pota- toes, salt & pepper. Adjust seasoning.
Measure flour, baking powder & salt in large bowl. Add water, egg & 1 Tbsp oil. Stir until dough holds together.
Put on a lightly floured surface & knead until smooth and elastic, using only enough extra flour to keep dough from sticking-this takes about 5 minutes. Put dough on lightly floured board, cover w/large bowl and let sit for 1/2 hour.
Divide dough into 4 pcs. Roll out each piece into a 12" square on a lightly floured sur- face. Cut in half to make two 6" wide strips. Brush lightly with oil. Spoon 1/8 of the filling down the center of each strip (the long way) Fold 1 long side over the filling & roll to the other side. This will make a long roll. Pinch edges together.
Repeat with rest of dough & filling. Put rolls on lightly oiled cooky sheets with the seam side down. Score with the blunt edge of a knife at 1-1/2" intervals, do not cut through. Brush with egg yolk mixture & bake in a preheated 375F oven for 30 minutes, or until golden brown.
Remove from oven & cut all the way through where scored. If you are freezing these, allow to cool to room temperature, place on cookie sheet & put in freezer un- til frozen.
Wrap well in plastic, over wrap with aluminum foil & return to freezer. To reheat, preheat oven to 375 degrees and bake for 15-20 minutes, or until hot.