In a large mixing bowl, whisk together the flour, 1/2 cup sugar, baking powder, salt, and 1/2 teaspoon cinnamon.
In another bowl, combine the melted butter, milk, egg, and vanilla extract.
Pour the wet ingredients into the dry ingredients and mix until just combined. Do not overmix.
Turn the dough onto a floured surface and gently knead it a few times until smooth.
Roll the dough out to about 1/2 inch thick.
Use a donut cutter or two round cookie cutters (one larger and one smaller) to cut out donut shapes.
Heat oil in a deep skillet or fryer to 350°F.
Carefully place the donuts in the hot oil, frying a few at a time for about 2-3 minutes on each side or until golden brown.
Remove the cronuts and drain on paper towels.
In a shallow dish, mix together 1/2 cup sugar and 1 teaspoon cinnamon.
While the cronuts are still warm, coat them in the cinnamon sugar mixture.
Serve immediately for the best texture and flavor.