Preheat oven to 200C/180C fan-forced. Grease a 5cm-deep, 16.5cm x 22cm (base) roasting pan.
Place potato in a large saucepan. Cover with cold water. Bring to the boil over high heat. Reduce heat to medium. Simmer for 12 minutes or until just tender. Drain. Set aside for 10 minutes or until cool enough to handle. Cut into quarters.
Meanwhile, melt butter in a saucepan over medium-high heat. Add garlic and thyme. Cook, stirring, for 30 seconds or until fragrant. Add our. Cook, stirring, for 1 minute or until bubbling. Gradually add milk, stirring constantly, until mixture is smooth and combined. Cook, stirring, for 4 to 5 minutes or until mixture boils and thickens. Add cream cheese, mustard and 1/2 cup colby cheese. Cook, stirring, for 1 to 2 minutes or until melted and smooth. Remove from heat.
Add potato to cheese mixture. Season with salt and pepper. Stir to combine. Transfer mixture to prepared pan. Top with remaining colby cheese. Bake for 30 to 40 minutes or until golden. Serve sprinkled with extra thyme.
Recipe courtesy of www.taste.com.au
Serving size 6