• Preheat oven to 350ºF. Line a 6-cup (8-1/2 x 4-1/2" or 9 x 5") loaf pan with parchment paper, leaving a 2" overhang.
• In a large bowl, whisk together flour, sugar, baking powder, baking soda, salt, cinnamon and nutmeg.
• In a separate bowl, whisk together oil, sour cream, milk and egg.
• Add oil mixture to dry ingredients and gently incorporate using a rubber spatula until about 80% combined. Fold in chopped apple to finish combining. (You don't want to over-stir or the cake will be tougher).
• Scrape batter into prepared loaf pan. Bake for 60-70 minutes, until internal temperature reaches 190ºF (or golden brown and tops spring back when lightly touched). Transfer to wire rack to cool.

For caramel

• Remove label from can of sweetened condensed milk and place in a medium saucepan. Fill with water to cover the can by 2". Bring to a simmer then reduce heat to low and maintain simmer for 2-3 hours, checking every 30 minutes to ensure the can is still submerged (adding more water as necessary).
• Remove from the hot water using canning tongs (or regular tongs, but be very careful not to drop it and splash hot water on yourself). Do not open the can until cool. Because it's under pressure, hot caramel may shoot out of the can if you pull the tab or puncture with a can opener while it's still hot.

To assemble

• Poke holes about 3/4" apart all over the cooled cake using a chopstick or the handle of a wooden spoon. Wiggle it gently back and forth to make a bit more space inside for the caramel.
• Whisk 1/2 cup caramel with 1 tbsp whipping cream. Use a piping bag and round tip to fill the holes in the cake (or spoon it over top and use the chopstick again to push it in, but it won't be as rippled inside).
• Whip remaining cream with 3 tbsp cooled caramel. Spread over cake just before serving.