Preheat your oven to 180°C (360°F) and lightly spray two 12-cup muffin tins with oil spray. Cut 24 circles from the shortcrust pastry sheets—I find using a cup or glass that's slightly larger than the muffin cup opening works perfectly. Press each pastry circle gently into the muffin cups, making sure it covers the bottom and sides evenly. Use a fork to prick the bottom of each shell several times; this prevents them from puffing up too much during the blind bake. Bake the pastry shells for 6–7 minutes until they're just set but still pale—you're not trying to fully cook them yet, just set their structure.

While the pastry shells bake, heat a large skillet over medium-high heat and add the chopped bacon. Cook, stirring occasionally, until the bacon is crispy and has rendered most of its fat, about 5–7 minutes. Add the minced garlic and diced onion to the pan and cook for just 1 minute, stirring constantly—you want the onion to soften slightly while the garlic releases its aroma, but not brown. Pour the contents into a fine-mesh strainer or colander to drain excess fat, then spread the mixture on a clean plate to cool slightly. I like to let it cool while the pastry finishes baking so it doesn't cook the eggs when combined.

In a large measuring jug or bowl, whisk together the room-temperature eggs, heavy cream, Dijon mustard, salt, and black pepper until completely smooth and well combined. The room-temperature eggs are key because they blend more smoothly with the cream and create a silkier custard. Whisk for about 1–2 minutes until the mixture is uniform in color and consistency. Set the jug aside while you finish assembling the quiches.

Remove the pastry shells from the oven and gently press down any puffed-up areas using the back of a spoon. Divide the cooled bacon mixture from Step 2 evenly among all 24 pastry cups, filling each about 1/4 of the way. Sprinkle the grated cheddar cheese evenly over the bacon in each cup. Carefully pour the custard mixture from Step 3 into each shell until it reaches just below the rim—fill slowly to avoid overfilling. Bake the quiches at 180°C for 18–20 minutes until the custard is just set but still slightly jiggly in the very center when you gently shake a tin. The residual heat will continue to set them as they cool.

Remove the quiches from the oven and let them rest in the tins for 5 minutes—this allows the filling to set completely and makes them easier to remove. Run a thin knife around the edges of each quiche to loosen them gently, then use a small spoon or offset spatula to lift them out. Serve warm or at room temperature. These mini quiches can be made ahead and reheated gently in a 150°C oven for about 5 minutes if needed.