In a small bowl, add butter, flour, baking powder, and 3 TBSP sugar out of the cup of sugar. Add the tsp. of cinnamon to the remainder of the cup of sugar and stir it up--save the rest of the sugar for later. Mix by hand. Pat the mixture in the bottom of an 8 x 8 x 2 glass or aluminum baking pan. Spread peach halves over the top. Pour the sugar/cinnamon over the top of the peaches. Pre-heat oven to 400 degrees. Bake for 15 minutes.
While it's baking, beat the 2 egg yolks by hand and mix in the sour cream. After 15 minutes, remove from oven and pour the egg yolk/sour cream mix over the top. Return to oven and bake for 30 additional minutes. Let it cool and then refrigerate.