Preheat oven to 350° (180° C) and thoroughly grease a 9-inch springform pan.
In a small bowl, sift together flour, baking soda, salt, cinnamon, and nutmeg.
In a large bowl, beat butter and sugar until smooth, then add eggs one at a time, followed by the vanilla.
Slowly mix the dry ingredients into the wet until just combined, then fold in apples and nuts if using.
Transfer batter to the prepared pan and bake for 35-40 minutes as you prepare the caramel.
Caramel: when cake has been baking for 30 minutes, start the caramel. Add brown sugar, half & half, and butter to a small saucepan over medium-low heat. Stir often until the mixture is smooth and fully combined, no need to bring to a full boil.
Remove cake from oven and pour caramel over the top. Return cake to oven for additional 10-15 minutes or until caramel is cracking and cake is cooked through the center.
Allow cake to cool at least 15 minutes before slicing.