8 tablespoons horchata
1 1/2 fluid ounces silver tequila
1 fluid ounce rum cream liqueur (such as RumChata®)
1/4 fluid ounce agave nectar
1/4 fluid ounce cinnamon whiskey (such as Fireball®)
1 teaspoon sweetened condensed milk, or to taste
1 dash ground cinnamon
Fill cocktail shaker with ice. Pour in horchata, tequila, rum cream liqueur, agave, and cinnamon whiskey. Shake until fully chilled. Dip rim of margarita glass in condensed milk; sprinkle with cinnamon. Pour horchata mixture into the glass.