Preheat oven to 375°F.: When the oven warms to 375°F you will notice a dry, toasty heat that helps the crust set quickly, promoting a crisp, golden edge. This temperature is ideal because it browns the crust while allowing the filling to bubble gently without burning. A common mistake is not preheating long enough, which can lead to soggy bottoms, so wait until the oven fully reaches temperature before baking.
Cut 4 6-inch rounds out of the pie crusts, and fit them into 4 5-inch mini pie dishes. Use a fork to crimp the edges, or use two hands to flute the edges of the pie crusts.: The visual cue you want is even, snug crusts pressed into each dish with no thin spots, and a decorative edge that will hold juices. The dough should feel cool and slightly firm while you work. If the pastry warms in your hands it becomes sticky and tears easily, so chill briefly if needed. Avoid overworking the dough, which can make it tough rather than flaky.
In a large bowl, stir together the Karo® Syrup, butter, sugar, corn starch, cinnamon and salt. Pour over apples and stir to coat.: At this stage the mixture should shine, the Karo® Syrup making the glaze glossy and the corn starch evenly distributed so no clumps remain. When you fold this into the apples , you want each piece to glisten with coating but not be swimming in liquid. If you see puddles of syrup, the corn starch may need more thorough mixing. A frequent error is adding the thickener directly to hot liquid which can form lumps, so whisk it into the sugar and syrup first for a smooth finish.
Evenly divide the apples between the prepared pie crusts.: Aim for uniform mounds so each mini pie bakes at the same rate, and the filling settles similarly across pies. You should hear the soft clink as apples nestle into the crust and see the glossy filling around them. Overfilling is a common issue, it can bubble over and make a sticky mess, so leave a small gap under the crust edge.
Prepare the crumb topping by mixing the flour, brown sugar, salt and butter with a fork until crumbs form. Top each pie with crumb topping.: Work until the mixture resembles coarse sand with pea sized clumps, so the topping toasts unevenly and gives contrast. The melted unsalted butter should bind the sugar and flour but not make it a paste. If the crumbs are too wet, they will steam instead of crisping, so add a touch more all purpose flour to dry them out slightly. Avoid packing the crumbs down, they should remain loose for a proper crunch.
Place mini apple pies on a large baking sheet lined with parchment paper or a silicone mat.: The sheet catches any bubbling filling, keeping your oven clean, and the parchment helps the bottoms heat evenly, reducing the chance of sticking. You should arrange them with some space so hot air circulates around each dish for even browning. A typical mistake is placing them too close together which can slow browning and create uneven results.
Bake pies in preheated oven for 40-45 minutes, until crusts are browned and apples are tender.: During baking you want to watch for a bubbling, syrupy filling and a deep golden top. The aroma will shift from raw fruit to caramelized sweetness, and the topping should develop toasted notes. If the crust browns too quickly, tent with foil to prevent burning while the filling finishes. Underbaked filling will be runny when cooled, so test by inserting a small knife; it should meet gentle resistance from cooked apple, not raw crunch.