Warm the sour cream and water to lukewarm in a microwave, or over very low heat, stirring constantly. Add the butter and stir until melted.
(If you're using a bread machine, as long as the butter isn't super-cold you can skip this step; just put the ingredients into the bucket of the machine in the order recommended by the manufacturer. You may also choose to bake the bread right in the machine; instead of programming for dough, program for basic or white bread.)
In another bowl, whisk together the lemon zest, flour, almond flour or almonds, sugar, yeast, and salt. Add the dry ingredients to the sour cream mixture, then mix in the eggs and flavor (or additional zest). Stir until the mixture becomes cohesive, then cover and set aside for 15 minutes.
Knead the dough -- by hand, electric mixer, food processor or bread machine -- until it's smooth and elastic, adding a small amount of water or flour to make a smooth dough, if needed.
Place it in a greased bowl, cover the bowl, and set the dough aside to rise for 1 1/2 to 2 hours, until it's doubled in bulk.
Turn the dough out onto a lightly greased surface and knead it gently a few times. Form it into a log, and place it in a lightly greased 13 x 4-inch pain de mie pan; or divide it in half, and place it in two lightly greased 8 1/2 x 4 1/2-inch bread pans. Cover the pans, and allow the dough to rise for 1 to 1 1/2 hours, until it's almost even with the top of the pan.
Bake the bread in a preheated 350 F oven for 22 to 26 minutes, or until its internal temperature registers 190 F on an instant-read thermometer. Remove from the oven, remove from the pans after 5 minutes, and cool completely on a rack.