With brown sugar.
A recipe somewhat more descriptive than the version in The Woman Suffrage Cook Book by Mrs. Hattie A. Burr from around 1886:
Anne B. Rogers.
Oatmeal pudding is, as you might imagine, prepared oatmeal. Another take, from the March 20, 1898 edition of the Boston Globe:
Oatmeal muffins made of cold oatmeal — 2 cups of oatmeal, 1/2 cup sugar, beat together, add 2 cups sweet milk and 2 cups of flour with 2 teaspoons of baking powder, little salt; beat all well together and bake in gem pans in quick oven, care to be taken to follow directions in putting together. We make 2-1/2 down in the morning for breakfast. Our family is larger than yours (9) and all good eaters.
From a box sold in Nampa, Idaho.
1 cup quick cooked oats
1 cup sour milk (buttermilk)
1/2 cup brown sugar
1/2 cup melted shortening
1 cup flour
1/2 tsp. salt
1 Tbsp. baking powder
1/2 tsp. baking soda
Soak oatmeal in sour milk 1 hour.
Add egg and beat well. Add sugar and mix.
Add cool shortening. Add flour (sifted with dry ingredients).
Pour into greased muffin tins; fill 2/3 full. Bake 400 deg. for 15 to 20 minutes.
Makes 1 dozen.