Maple syrup apple cake

I stole this cake from here: www.seasonsandsuppers.ca/upside-down-maple-apple-cake/

I've now made it twice without exactly following the recipe...

1 cup pure maple syrup

3 2 Granny Smith apples—peeled, cored and quartered, then cutting each quarter into 3 equal slices.

• 2 cups all-purpose flour
• 1 teaspoon baking powder
• 1/2 teaspoon baking soda
• 1 teaspoon salt
• 3 large eggs
• 3/4 cup buttermilk
• 1 tablespoon pure vanilla extract
• 3/4 cup (1 1/2 sticks) unsalted butter, softened
• 1 1/3 cups sugar
• Vanilla Ice Cream and a bit more maple syrup, for serving

1. Preheat the oven to 350° F. Butter a 10-inch round cake pan with 3-inch high sides. Place a round of parchment paper on the bottom. Set aside. 
2. If using a 10-inch spingform pan: Take a large sheet of foil or parchment paper (or two pieces joined together as best as you can). Press down onto the bottom and sides of the pan, creasing as necessary to have reasonably smooth sides. Alternately, you can just cover the bottom with parchment or foil and then assemble your springform. The extra bulk is sometimes enough to stop stuff from leaking out. To test, pour an inch of water into it and see if any leaks out. Which ever method you use, be sure to place the prepared pan on top of a baking sheet (to catch any leaks when it bakes), then set aside.
3. In a large saucepan, bring the maple syrup to a boil over high heat, then simmer over low heat until very thick and reduced to 3/4 cup, about 20 minutes. While the syrup is simmering, you can peel and cut your apples. Pour the thickened syrup into the prepared pan. Arrange the apples in the pan in 2 concentric circles, overlapping them slightly.
4. In a bowl, whisk the flour, baking powder, baking soda and salt. In a small bowl, whisk the eggs with the buttermilk and vanilla.
5. In the bowl of a stand mixer fitted with the paddle attachment, beat the butter and sugar by hand at medium speed until fluffy, about 3 minutes. Beat in the dry and wet ingredients in 3 alternating batches until the batter is smooth. scrape down the side of the bowl.
6. Pour the batter over the apples and spread it into an even layer. Bake the cake for about 35-40 minutes if baking in a cake pan or up to 45-55 minutes if baking in a springform pan placed on a baking sheet. Watch it closely after 30 minutes of baking in any case. You’ll want the top to be puffed and golden brown, and a tester inserted in the centre should come out clean. Let the cake cool in the pan, on a cooling rack for 45 minutes.