Combine the yeast with tepid milk and let it stand for 10 minutes to activate.

Sift flour into a bowl and create a well in the center.

Pour the yeast mixture into the flour well and mix to form a sponge.

Cover the sponge and let it rise in a warm place for about 1 hour, or until doubled in bulk.

Work in the rolled oats, mashed potatoes (if using), butter or lard, and salt into the sponge.

Knead the dough until bubbles appear, approximately 15 minutes.

Divide the dough into two equal parts.

Butter two 8 1/2 by 4 1/2 inch loaf pans.

Lightly press the dough into the prepared loaf pans.

Let the loaves rise in a warm place for about 30 minutes, or until the top of the dough is about 1/2 inch above the rims of the pans.

Preheat oven to 350°F (175°C).

Bake in the preheated oven for 1 hour to 1 hour and 15 minutes, or until golden brown.