Preheat your oven to 350°F (175°C) and line a 9-inch square baking pan with parchment paper, leaving some overhang for easy removal.
Peel, core, and dice two of the apples into 1/2-inch cubes. Slice the remaining apple into thin wedges for decorative topping. Toss the diced apples with 1 tablespoon of lemon juice to prevent browning.
In a medium bowl, whisk together the flour, baking powder, baking soda, salt, cinnamon, nutmeg, and cloves until evenly distributed.
In a large bowl, beat the softened butter and brown sugar with an electric mixer until light and fluffy, about 3-4 minutes.
Add eggs one at a time, beating well after each addition. Stir in the Greek yogurt and vanilla extract until smoothly incorporated.
Gradually fold the dry ingredients into the wet ingredients until just combined. Do not overmix.
Gently fold in the diced apples, ensuring they're evenly distributed throughout the batter.
Pour the batter into your prepared pan and arrange the apple slices on top in a decorative pattern.
Bake for 40-45 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs. If edges brown too quickly, tent with foil after 30 minutes.
While the cake is baking, prepare your toffee sauce. In a medium saucepan over medium heat, melt the butter. Add the brown sugar and stir until dissolved, about 2-3 minutes.
Gradually whisk in the cream, being careful as mixture may sputter. Bring to a gentle boil, then reduce heat and simmer for 5 minutes until slightly thickened. Remove from heat and stir in salt and vanilla.
When the cake is done, allow it to cool in the pan for 10 minutes before lifting out using the parchment overhang.
While still warm, poke holes throughout the cake with a skewer and pour half the warm toffee sauce over the top, allowing it to soak in. Reserve the remaining sauce for serving.