Step 1

Preheat the oven to 350 degrees F.

Step 2

Butter 2 (9 by 5 by 3-inch) loaf pans, using the heaping tablespoon of the butter.

Step 3

Cream the remaining butter and the sugar in the bowl of an electric mixer on low speed until light and fluffy. Scrape down the sides with a rubber spatula.

Step 4

In a separate mixing bowl, beat together the egg yolks with the vanilla until light and frothy. With the electric mixer on medium-low, gradually add the egg yolk mixture to the butter and sugar mixture and mix for about 4 minutes.

Step 5

In another bowl, combine the flour, baking powder, and salt. With the electric mixer on medium speed, alternately add the flour mixture, a third at a time, and the egg whites, a third at a time, to the butter and egg mixture, beating for 2 minutes between each addition. Scrape down the sides of the bowl as you mix. Add the lemon zest during the last 2 minutes of mixing.

Step 6

Divide the batter equally between the pans. To 1 of the cakes, add the crumbled pralines and the rum to the batter and gently stir to mix evenly; leave the other plain. Bake the plain cake for about 1 hour, the praline cake for about 1 hour and 10 minutes. Both should be golden when done and firm to the touch.

Step 7

The cakes can be stored by wrapping them in waxed paper, then plastic wrap, then in foil. They do not need to be refrigerated.

Step 8

In a heavy saucepan, over medium heat, combine the sugar, brown sugar, corn syrup, butter, salt and condensed milk. With a wooden spoon, stir until the sugar dissolves. Continue to cook, stirring, until smooth and light brown, about 8 minutes. Add the vanilla and pecans and continue to cook, stirring, until the mixture reaches 234 to 240 degrees F. on a candy thermometer or the soft ball stage, that is, when a bit dropped into cold water forms a soft ball that flattens. Remove from the heat and drop by the spoonful onto waxed paper. Let cool. Remove from the paper with a thin knife.