In a large mixing bowl sift together the flour, cinnamon, ginger, cardamom, nutmeg, and baking powder.

In a separate bowl whisk together the eggs, melted butter, sourdough discard, and sugar.

Add the dry ingredients to the wet ingredients a little at a time, mixing until everything is incorporated and no lumps remain. Your batter will be thick but don't worry, the apples add moisture while your cake bakes.

Use a pairing knife or vegetable peeler to peel your apples.

Once the apples are peeled, cut each apple into fourths and then remove the core.

Cut each fourth or apple in half lengthwise, this will give you eighths.

Slice each eighth crosswise into ¼ inch pieces.Its important your apple slices are close in size to ensure they cook evenly.

Once your apples are sliced fold them into the cake batter.

In a small mixing bowl stir together the rolled oats, flour, and sugar until everything is evenly incorporated.

Using a fork or pastry blender, cut the butter into your dry ingredients until the largest bits of butter are no larger than a pea.

Toss the mixture with a fork or by hand to ensure all the butter if fully coated in the flour mixture.

Pour your batter into a well greased 9" springform pan. Spread the batter until it is level and top evenly with the streusel mixture.

Bake on the center rack of a 350°F(180°C) preheated oven for 60 minutes. A toothpick inserted into the center of the cake will come out clean when it is fully cooked.

In a small bowl whisk together the egg yolks, sugar, milk, and vanilla.

Add the mixture to a small sauce pan and turn the burner to medium low heat. It's important to not preheat your pan or burner before adding the custard.

As your custard comes to heat, stir consistently to prevent curdling and ensure a smooth sauce. Your custard is ready when it thickens to the consistency of a gravy, about 6 -10 minutes.

Once your custard has thickened, remove it from the heat and immediately transfer it to a gravy boat or jar to prevent overcooking.

Slice your your sourdough Irish Apple Cake and top with warm custard sauce before serving.