Combine all purpose flour, lard, and salt in a mixing bowl. Cut lard into the all-purpose flour with a pastry blender until it resembles coarse breadcrumbs. Gently knead until dough comes together. This should only take 1 minute.

Shape dough into a 4 in x 4 in square and wrap with plastic.

Combine all-purpose flour, lard, salt, and egg in the same mixing bowl. Add about half the ice cold water. Cut in the lard, butter, and egg into the all-purpose flour with a pastry blender. Add more ice cold water bit by bit until it resembles coarse breadcrumbs. You may or may not use all of the water. Gently knead until the dough comes together.

Transfer dough to a lightly floured work surface and continue to knead until dough is more or less smooth, about 1 to 2 minutes. Shape dough into a 6 in x 6 in square and wrap with plastic.

Place both dough in the refrigerator for 30 minutes. In the meantime, line 2 baking trays with parchment paper.

Heat vegetable oil in a medium size pan over medium heat. Saute garlic and onion for 2 to 3 minutes.

Add char siu and hoisin sauce. Stir and add water. Cover and cook for 2 minutes. Remove lid, add frozen green peas, cover, and continue to cook for another 2 minutes.

Pour in corn starch mixture and allow sauce to thicken. Turn off stove and allow filling to cool completely.

After 30 minutes, remove both dough from the refrigerator. Roll out the water dough into a 6 in x 12 in rectangle and place the oil dough in the center.

Fold the bottom ⅓ over the oil dough and the top ⅓ to overlap the bottom ⅓. Rotate the dough 90⁰ and flip it over with seams facing down. Roll it out into a rectangle of about 6 in x 12 in.

Flip the dough over with seams facing up. Fold the bottom ⅓ of dough over the middle. Then, fold the top ⅓ over the bottom ⅓. Rotate 90⁰ and flip dough over with seams facing down. Roll it out into a rectangle of about 6 in x 12 in.

Flip the dough over with seams facing up. Fold the bottom ⅓ of dough over the middle. Then, fold the top ⅓ over the bottom ⅓. Wrap with plastic and let dough rest in the refrigerator for 15 minutes.

After 15 minutes, remove dough from refrigerator and cut it in half crosswise.

Roll one portion of the dough out into roughly 10 in x 17 in rectangle and about 1/8 inch thick. Cut out 8 pieces of dough with a 4 inch round cookie cutter.

Do the same for the other piece of dough.

Gather all the leftover dough (after the round cut-outs) into a rectangular bundle. Roll it out and repeat the folding and rolling process as above. You should be able to get another 4 wrappers from this, giving you a total of 20 wrappers.

Place wrappers in a container so that they will not dry out.

Flatten the edges of a piece of dough wrapper with both thumbs and index fingers or you can roll it out with a small rolling pin.

Place the dough wrapper on your palm and a rounded tablespoon of filling in the middle of wrapper. Gather and pleat the edges with your thumb and index finger. Then twist and pinch to seal.

Place seam side up onto prepared baking tray.

Preheat oven to 400⁰F/200⁰C. Apply egg wash on each shaped and formed bun and sprinkle some sesame seeds on the top.

Transfer baking trays to preheated oven. Bake for 30 to 35 minutes until golden brown.

When baking is complete, turn off the oven and remove baking trays from the oven. Allow siew paus to cool on the counter.