Using an electric mixer (stand or handheld) cream the butter and sugar together. Add the vanilla extract and mix together well.
In a separate bowl, combine the flour and salt, and stir well to blend.
Add the flour mixture to the mixer, a little at a time, blending between additions, until all the flour has been added and the ingredients are well mixed. Scrape down the sides of the bowl and blend.
Cover the mixing bowl and place it in the refrigerator for 30 minutes, to chill the dough.
Preheat oven to 180C/350F/Gas 4 and line a cookie sheet with parchment/baking paper.
Roll the cookie dough into tablespoon-size balls, and place them on the parchment paper. When the cookie sheet(s) is full, use your thumb, or knuckle to make an indentation in the center of each cookie ball.
Bake for 20 minutes, or until the cookies are light golden brown. Remove the cookies to a wire rack and allow them to cool completely.
When the cookies are completely cooled, place the sprinkles in a shallow dish and set aside.
Melt half of the white chocolate in a microwave-safe bowl in the microwave in 20-second intervals, stirring well in between until the chocolate is completely melted.
Dip the bottoms of the cookies in the chocolate, and immediately into the sprinkles, and place them on parchment paper to set.
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When all the cookies have been dipped, melt the rest of the white chocolate in the microwave, (following the same directions as in step 9) and fill the center of each cookie with the melted chocolate.
Place three Reindeer corns on the top of the white chocolate in the center of each cookie.
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Leave the cookies to sit for 1 to 2 hours so that the chocolate can set. Then serve or store in an airtight container for up to 4 days.