Grease a 9-by-5-by-3-inch loaf pan and dust with flour.
Peel and dice the peaches; you should have about 3 cups of diced peaches. Put the diced peaches in a saucepan with the peach nectar or liqueur. Bring to a simmer and continue to cook for about 6 to 8 minutes, or until the peaches are tender. Remove the pan from the heat and add the vanilla extract; set aside.
In a mixing bowl with an electric mixer, beat the softened butter and sugar until light and creamy. Add the eggs, one at a time, beating well after each addition.
Combine the flour, baking powder, salt, soda, and cinnamon in another bowl; stir to blend. Stir the dry ingredients into the creamed mixture, alternating with the peach mixture. Stir just until blended; do not overmix.
Spread the batter in the prepared loaf pan.
Bake for 55 to 65 minutes, or until a toothpick inserted into the center of the bread comes out clean.
Remove to a rack and let it cool for 10 minutes before turning it out onto the rack to cool completely.